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95S  Congress  I  COMMITTEE  PRINT 

2d  Session  J 



Prepared  at  the  Request  of 

Hox.  Howard  W.  Cannon,  Chairman 


MAY  1978 

Printed  for  the  use  of  the 
Committee  on  Commerce,  Science,  and  Transportation 

U.S.  government  printing  office 

34-857  WASHINGTON  :  1978 


HOWARD  W.  CANNON,  Nevada,  Chairman 

WARREN  G.  MAGNUSON,  Washington 
RUSSELL  B.  LONG,  Louisiana 
ERNEST  F.  HOLLINGS,  South  Carolina 
DANIEL  K.  INOUYE,  Hawaii 
ADLAI  E.  STEVENSON,  Illinois 
WENDELL  H.  FORD,  Kentucky 
JOHN  A.  DURKIN,  New  Hampshire 
DONALD  W.  RIEGLE,  Jr.,  Michigan 

Aubrey  L.  Sarvis,  Staff  Director  and  Chief  Counsel 

Edwin  K.  Hall,  General  Counsel 
Malcolm  M.  B.  Sterrett,  Minority  Staff  Director 

JAMES  B.  PEARSON,  Kansas 
ROBERT  P.  GRIFFIN,  Michigan 
TED  STEVENS,  Alaska 
HARRISON  H.  SCHMITT,  New  Mexico 
JOHN  C.  DANFORTH,  Missouri 


U.S.  Senate, 

Committee  on  Commerce,  Science,  and  Transportation, 

November  15, 1978. 
To  the  members  of  the  Committee  on  Commerce.  Science,  and 
Transportation,  U.S.  Senate: 

I  am  pleased  to  transmit  herewith  for  your  information  and  use  the 
following  report  on  "Weather  Modification:  Programs,  Problems, 
Policy,  and  Potential." 

The  report  was  prepared  at  my  request  by  the  Congressional  Re- 
search Service  under  the  direction  of  Dr.  Robert  Morrison,  Specialist 
in  Earth  Sciences,  Science  Policy  Research  Division.  We  thank  Dr. 
Morrison  and  the  others  involved  in  the  study  for  their  extremely 
thorough  and  scholarly  report.  Substantial  material  on  almost  all 
areas  of  weather  modification  are  included  and  the  report  will  provide 
the  committee  with  an  excellent  reference  source  for  future  delibera- 
tions on  the  subject. 

The  completion  of  the  report  is  particularly  timely  due  to  the  up- 
coming recommendations  expected  from  the  Weather  Modification 
Advisory  Board  and  the  Department  of  Commerce  (as  directed  by 
Public  Law  94-490)  on  the  future  Federal  role  in  weather 

James  B.  Pearson, 
Ranking  minority  member. 



U.S.  Senate, 

Committee  on  Commerce,  Science,  and  Transportation, 

Washington,  D.C.,  July  30, 1976. 

Dr.  Norman  A.  Beckman, 

Acting  Director,  Congressional  Research  Service, 
Library  of  Congress,  W ashington,  D.C. 

Dear  Dr.  Beckman:  Weather  modification,  although  a  relatively 
young  science,  has  over  the  years  stimulated  great  interest  within  the 
scientific,  commercial,  governmental,  and  agricultural  communities. 
Such  responses  are  readily  understandable.  Weather-related  disasters 
and  hazards  affect  virtually  all  Americans  and  annually  cause  untold 
human  suffering  and  loss  of  life  and  result  in  billions  of  dollars  of  eco- 
nomic loss  to  crops  and  other  property.  While  weather  modification 
projects  have  been  operational  for  nearly  25  years  and  have  been 
shown  to  have  significant  potential  for  preventing,  diverting,  moderat- 
ing, or  ameliorating  the  adverse  effects  of  such  weather  related  disas- 
ters and  hazards,  I  am  greatly  concerned  regarding  the  lack  of  a 
coordinated  Federal  weather  modification  policy  and  a  coordinated 
and  comprehensive  program  for  weather  modification  research  and 
development.  This  fact  is  all  the  more  disturbing  in  view  of  the  mani- 
fest needs,  and  benefits,  social  and  economic,  that  can  be  associated  with 
weather  modification  activities.  These  deficiencies  in  our  Federal  orga- 
nizational structure  have  resulted  in  a  less  than  optimal  return  on  our 
investments  in  weather  modification  activities  and  a  failure,  with  few 
exceptions,  to  recognize  that  much  additional  research  and  develop- 
ment needs  to  be  carried  out  before  weather  modification  becomes  a 
truly  operational  tool. 

Reports  and  studies  conducted  by  such  diverse  organizations  as  the 
National  Academy  of  Sciences,  the  National  Advisory  Committee  on 
Oceans  and  Atmosphere,  the  General  Accounting  Office,  and  the 
Domestic  Council  have  highlighted  the  lack  of  a  comprehensive  Federal 
weather  modification  policy  and  research  and  development  program. 
Hearings  that  I  chaired  in  February  of  this  year  reinforced  my  con- 
cerns regarding  the  wisdom  of  our  continued  failure  to  implement  a 
national  policy  on  this  very  important  issue. 

I  am  therefore  requesting  the  Congressional  Research  Service  to 
prepare  a  comprehensive  report  on  weather  modification.  This  report 
should  include  a  review  of  the  history  and  existing  status  of  weather 
modification  knowledge  and  technology;  the  legislative  history  of 
existing  and  proposed  domestic  legislation  concerning  weather  mod- 
ification; socio-economic  and  legal  problems  presented  by  weather 
modification  activities;  a  review  and  analysis  of  the  existing  local, 
State,  Federal,  and  international  weather  modification  organizational 



structure:  international  implications  of  weather  modification  activi- 
ties: and  a  review  and  discussion  of  alternative  U.S.  and  international 
weather  modification  policies  and  research  and  development  programs. 

If  you  have  any  questions  with  respect  to  this  request,  please  contact 
Mr.  Gerry  J.  Kovach,  Minority  Staff  Counsel  of  the  Senate  Commerce 
Committee.  He  has  discussed  this  study  with  Mr.  Robert  E.  Morrison 
and  Mr.  John  Justus  of  the  Science  Policy  Division,  Congressional 
Research  Service. 

Very  truly  yours, 

James  B.  Pearsox, 

U.S.  Senator. 


The  Library  of  Congress, 
congressional  research  service, 

Washington,  D.C.,  June  19, 1978. 

Hon.  James  B.  Pearson, 

Committee  on  Commerce,  Science,  and  Transportation, 
U.S.  Senate,  Washington,  D.C. 

Dear  Senator  Pearson:  The  enclosed  report,  entitled  "Weather 
Modification:  Programs,  Problems,  Policy,  and  Potential,"  has  been 
prepared  by  the  Congressional  Research  Service  in  response  to  your 

The  study  reviews  the  history,  technology,  activities,  and  a  number 
of  special  aspects  of  the  field  of  weather  modification.  Activities 
discussed  are  those  of  the  Federal,  State,  and  local  governments,  of 
private  organizations,  and  of  foreign  nations.  Consideration  is  given 
to  international,  legal,  economic,  and  ecological  aspects.  There  are 
also  an  introductory  chapter  which  includes  a  summary  of  issues,  a 
chapter  discussing  inadvertent  weather  and  climate  modification,  and 
a  chapter  summarizing  recommendations  from  major  Federal  policy 

The  study  has  been  coordinated  by  Dr.  Robert  E.  Morrison,  Special- 
ist in  Earth  Sciences,  Science  Policy  Research  Division,  who  also 
prepared  chapters  1,  2,  3,  5,  7,  8,  and  9  as  well  as  the  Summary  and 
Conclusions.  Mr.  John  R.  Justus,  Analyst  in  Earth  Sciences,  and 
Dr.  James  E.  Mielke,  Analyst  in  Marine  and  Earth  Sciences,  both 
of  the  Science  Policy  Research  Division,  contributed  chapters  4  and 
6,  respectively.  Chapter  10  was  prepared  by  Mrs.  Lois  B.  McHugh, 
Foreign  Affairs  Analyst,  Foreign  Affairs  and  National  Defense  Di- 
vision. Chapter  11  was  written  jointly  by  Mrs.  Nancy  Lee  Jones, 
Legislative  Attorney,  and  Mr.  Daniel  Hill  Zaf ren,  Specialist  in  Ameri- 
can Public  Law,  both  of  the  American  Law  Division.  Dr.  Warren 
Viessman,  Jr.,  Senior  Specialist  in  Engineering  and  Public  Works, 
contributed  chapter  12;  and  Mr.  William  C.  JolW,  Analyst  in  En- 
vironmental Policy,  Environment  and  Natural  Resources  Division, 
was  responsible  for  chapter  13.  In  addition,  appendixes  C,  F,  Q,  and  R 
were  assembled  by  Mrs.  McHugh ;  appendixes  D  and  S  were  prepared 
by  Mrs.  Jones;  and  information  in  the  remaining  appendixes  was 
collected  by  Dr.  Morrison. 

I  trust  that  this  report  will  serve  the  needs  of  the  Committee  on 
Commerce,  Science,  and  Transportation  as  well  as  those  of  other 
committees  and  individual  Members  of  Congress  who  are  concerned 
with  weather  modification.  On  behalf  of  the  Congressional  Research 
Service,  I  wish  to  express  my  appreciation  for  the  opportunity  to 
undertake  this  timely  and  worthwhile  assignment. 

Gilbert  Gtjde, 



Digitized  by  the  Internet  Archive 
in  2013 



Letter  of  transmittal   in 

Letter  requesting  study   v 

Letter  of  submittal   vn 

Summary  and  conclusions   xix 

Chapter  1 

Introduction  and  summary  of  issues   1 

Perspective   1 

Situation   1 

Advantages   3 

Timeliness   5 

Definitions  and  scope  of  report   7 

Summary  of  issues  in  planned  weather  modification   9 

Technological  problems  and  issues   9 

Governmental  issues   12 

The  role  of  the  Federal  Government   12 

Roles  of  State  and  local  governments   14 

Legal  issues   15 

Private  rights  in  the  clouds   15 

Liability  for  weather  modification   16 

Interstate  legal  issues   17 

International  legal  issues   17 

Economic  issues   18 

Issues  complicating  economic  analyses  of  weather  modifica- 
tion  18 

Weather  modification  and  conflicting  interests   19 

Social  issues   19 

Social  factors   20 

Need  for  public  education  on  weather  modification   21 

Decisionmaking   22 

International  issues   23 

Ecological  issues   24 

Chapter  2 

History  of  weather  modification   25 

Introduction   25 

History  of  weather  modification  prior  to  1946   26 

Prescientific  period   26 

Early  scientific  period   27 

Development  of  scientific  fundamentals   32 

Early  cloud-seeding  experiments   34 

Weather  modification  since  1946   35 

Chronology   35 

Langmuir,  Schaefer,  and  Vonnegut   37 

Research  projects  since  1947   39 

Project  Cirrus   39 

The  Weather  Bureau  cloud  phvsics  project   41 

The  U.S.  experiments  of  1953-54   42 

Arizona  Mountain  cumulus  experiments   44 

Project  Whitetop   44 

Climax  experiments   45 

Lightning  suppression  experiments   46 

Fog  dispersal  research   46 

Hurricane  modification.   46 

Hail  suppression   46 

Foreign  weather  modification  research   47 

Commercial  operations   48 

History  of  Federal  activities,   committees,   policy  studies,  and 

reports   53 



Chapter  3 


Technology  of  planned  weather  modification   55 

Introduction   55 

Assessment  of  the  status  of  weather  modification  technology   56 

Classification  of  weather  modification  technologies   61 

Principles  and  status  of  weather  modification  technologies   62 

Precipitation  augmentation   64 

Cumulus  clouds   66 

Cumulus  modification  experiments   67 

Effectiveness  of  precipitation  enhancement  research  and 

operations   69 

Results  achieved  through  cumulus  modification   70 

Recent  advances  in  cumulus  cloud  modification   71 

Orographic  clouds  and  precipitation   71 

Orographic  precipitation  modification   75 

Orographic  seeding  experiments  and  seedability  criteria   77 

Operational  orographic  seeding  projects   81 

Results  achieved  through  orographic  precipitation  modifi- 
cation  82 

Hail  suppression   84 

The  hail  problem   84 

Modification  of  hail   86 

Hail  seeding  technologies   87 

Evaluation  of  hail  suppression  technology   88 

Surveys  of  hail  suppression  effectiveness   89 

Conclusions  from  the  TASH  study   91 

Dissipation  of  fog  and  stratus  clouds   92 

Cold  fog  modification   93 

Warm  fog  modification   93 

Lightning  suppression   96 

Lightning  modification   98 

Evaluation  of  lightning  suppression  technology   99 

Modification  of  severe  storms   101 

Hurricanes   101 

Generation  and  characteristics  of  hurricanes   104 

Modification  of  hurricanes   108 

Tornadoes   112 

Modification  of  tornadoes   113 

Technical  problem  areas  in  planned  weather  modification   115 

Seeding  technology   115 

Evaluation  of  weather  modification  projects   118 

Extended  area  effects  of  weather  modification   124 

Approaches  to  weather  modification  other  than  seeding   129 

Research  needs  for  the  development  of  planned  weather  modification-  131 

General  considerations   131 

Recommendations  from  the  1973  National  Academv  of  Sciences 

study  i   134 

Recommendations  of  the  Advanced  Planning  Group  of  NOAA__.  136 

Summary  of  Federal  research  needs  expressed  by  State  officials.  138 
Research  recommendations  of  the  AMS  Committee  on  Weather 

Modification   139 

Research  recommendations  related  to  extended  area  and  time 

effects   143 

Chapter  4 

Inadvertent  weather  and  climate  modification   145 

Introduction   145 

Terminology   145 

Climate   145 

Climatic  fluctuation  and  climatic  change   146 

Weather   146 

Weather  modification   146 

Climate  modification   146 

Planned  climate  modification   147 

Inadvertent  climate  modification   148 



Background   149 

Historical  perspective   149 

Understanding  the  causes  of  climatic  change  and  variability   151 

The  concept  of  climatic  change  and  variability   152 

When  and  how  do  climatic  changes  occur   154 

The  facts  about  inadvertent  weather  and  climate  modification   156 

Airborne  particulate  matter  and  atmospheric  turbidity   156 

Do  more  particles  mean  a  warming  or  cooling?   157 

Sources  of  atmospheric  particulates:  Natural  vs.  manmade..  158 

Atmospheric  processes  affected  by  particulates   159 

The  La  Porte  weather  anomaly:  Urban  climate  modification.  162 

Carbon  dioxide  and  water  vapor   164 

Increases   in   atmospheric   carbon   dioxide  concentration: 

What  the  record  indicates   164 

Predicting  future  atmospheric  carbon  dioxide  levels   166 

Sources  and  sinks  for  carbon  dioxide   168 

Atmospheric  effects  of  increased  carbon  dioxide  levels   169 

Implications  of  increasing  atmospheric  carbon  dioxide  con- 
centrations  169 

Implications  of  a  climatic  warming   170 

Carbon  dioxide  and  future  climate:  The  real  climate  vs. 

"model  climate"   171 

Ozone  depletion   172 

Concerns  regarding  ozone  destruction   172 

Action  by  the  Government  on  the  regulation  of  fluorocar- 

bons   175 

Climatic  effects  of  ozone  depletion   176 

Waste  heat   177 

The  urban  "Heat  Island"   177 

Albedo   179 

Large-scale  irrigation   180 

Recapitulation   181 

Issues  in  inadvertent  weather  and  climate  modification   184 

Climatic  barriers  to  long-term  energy  growth   184 

Thoughts  and  reflections — Can  we  contemplate  a  fossil-fuel-free 

world?   185 

Research  needs  and  deficiencies   186 

Chapter  5 

Federal  activities  in  weather  modification   193 

Overview  of  Federal  activities..--    '—  —   193 

Legislative  and  congressional  activities   194 

Federal  legislation  on  weather  modification   194 

Summary   194 

The  Advisory  Committee  on  Weather  Control   195 

Direction  to  the  National  Science  Foundation   196 

Reporting  of  weather  modification  activities  to  the  Federal 

Government   197 

The  National  Weather  Modification  Policy  Act  of  1976   198 

Congressional  direction  to  the  Bureau  of  Reclamation   201 

Proposed  Federal  legislation  on  weather  modification   203 

Summary   203 

Legislation  proposed  in  the  94th  Congress  and  the  95th 

Congress,  1st  sessions   205 

Other  congressional  activities   207 

Resolutions  on  weather  modification   207 

Hearings   208 

Studies  and  reports  by  congressional  support  agencies   209 

Activities  of  the  executive  branch   209 

Introduction   209 

Institutional  structure  of  the   Federal  weather  modification 

program   210 

Current  status  of  Federal  organization  for  weather  modifica- 
tion  210 



Federal  structure;  1946-57   214 

Federal  structure;  1958-68   215 

Federal  structure;  1968-77   216 

Future  Federal  organization  for  weather  modification   216 

Coordination  and  advisory  mechanisms  for  Federal  weather 

modification  programs   221 

Introduction   221 

The  Interdepartmental  Committee  for  Atmospheric  Sciences 

(ICAS)   222 

The   National   Academv   of   Sciences/Committee   on  At- 
mospheric Sciences  (N AS/CAS)   226 

The  National  Advisory  Committee  on  Oceans  and  Atmos- 
phere (NACOA)   227 

Other  coordination  and  advisory  mechanisms   228 

Weather  Modification  Advisory  Board   231 

Weather  modification  activities  reporting  program   232 

Background  and  regulations   232 

Reporting  of  Federal  activities   233 

Summary  reports  on  U.S.  weather  modification  activities   233 

Federal  studies  and  reports  on  weather  modification   234 

Introduction   234 

Studies  of  the  early  1950's   235 

Advisory  Committee  on  Weather  Control   236 

National  Academy  of  Sciences  studies   237 

Studies  bv  the  Interdepartmental  Committee  for  Atmos- 
pheric Sciences  (ICAS)   238 

Domestic  Council  study   239 

Policy  and  planning  reports  produced  by  Federal  agencies   239 

Federal  programs  in  weather  modification   241 

Introduction  and  funding  summaries   241 

Department  of  the  Interior   246 

Introduction   246 

Project  Skywater;  general  discussion   247 

The  Colorado  River  Basin  Pilot  Project  (CRBPP)   254 

The  High  Plains  Cooperative  Program  (HIPLFX)   258 

The  Sierra  Cooperative  Pilot  Project  (SCPP)   263 

Drought  mitigation  assistance   266 

National  Science  Foundation   267 

Introduction  and  general   267 

Weather  hazard  mitigation   274 

Weather  modification  technology  development   282 

Inadvertent  weather  modification   283 

Societal  utilization  activities   287 

Agricultural  weather  modification   288 

Department  of  Commerce   290 

Introduction  and  general  discussion   290 

The  Florida  Area  Cumulus  Experiment  (FACE)   292 

Project  Stormfurv   296 

Research  Facilities  Center  (RFC)   300 

Global  Monitoring  for  Climatic  Change  (GMCC)   301 

Lightning  suppression   302 

Modification  of  extratropical  severe  storms   302 

Department  of  Defense   303 

Introduction   303 

Air  Force  fog  dispersal  operations   303 

Army  research  and  development   304 

Navy  research  and  development   304 

Air  Force  research  and  development   305 

Overseas  operations   307 

Department  of  Transportation   308 

Department  of  Agriculture   309 

Department  of  Energy   310 


Chapter  6 

Review  of  recommendations  for  a  national  program  in  weather  modifica-  Page 

tion   313 

Introduction   ^Jy 

Summaries  of  major  weather  modification  reports   314 

Final  report  of  the  Advisory  Committee  on  Weather  Control —  314 
Weather  and  climate  modification:  Report  of  the  Special  Com- 
mission on  Weather  Modification   315 

Weather  and  climate  modification:  Problems  and  prospects   317 

A  recommended  national  program  in  weather  modification   318 

A  national  program  for  accelerating  progress  in  weather  modifica- 
tion  320 

Weather  and  climate  modification:  Problems  and  progress   321 

Annual  reports  to  the  President  and  Congress  by  NACOA   323 

Need  for  a  national  weather  modification  research  program   324 

The  Federal  role  in  weather  modification   325 

Trends  and  analysis   326 

Chapter  7 

State  and  local  activities  in  weather  modification   331 

Overview  of  State  weather  modification  activities   331 

Introduction   331 

North  American  Interstate  Weather  Modification  Council   333 

Survey  and  summary  of  State  interests  and  activities  in  weather 

modification   340 

State  contacts  for  information  on  weather  modification  activities.  343 

Non-Federal  U.S.  weather  modification  activities   343 

Analysis  of  calendar  year  1975  projects   344 

Preliminary  analysis  of  projects  for  calendar  years  1976-77_  347 
General  discussion  of  local  and  regional  weather  modification  policy 

activities  „  348 

Weather  modification  activities  within  particular  States   351 

California   352 

State  weather  modification  law  and  regulations   352 

Weather  modification  projects   353 

State-sponsored  emergency  projects   356 

Illinois   358 

Illinois  weather  modification  law  and  its  administration   358 

Operational  projects   359 

Research  activities   360 

Kansas   361 

Kansas  Weather  Modification  Act   361 

Research  activities   362 

Operational  activities   364 

Emergenc}-  Drought  Act  of  1977   364 

North  Dakota   365 

Weather  modification  law  and  administration  of  regulations-  365 

Authority  and  organization  for  local  projects   370 

North  Dakota  operational  projects  in  1975  and  1976   371 

South  Dakota   376 

Utah   381 

Washington   382 

Chapter  8 

Private  activities  in  weather  modification   385 

Introduction   385 

Commercial  weather  modifiers   386 

Scope  and  significance  of  contract  activities   386 

Summary  of  contract  services   386 

Evaluation  and  research  by  commercial  firms   388 

Participation  in  Federal  research  programs   389 

Weather  modification  organizations   389 

Professional  organizations   389 

Weather  Modification  Association   390 

American  Meteorological  Society   395 



Opposition  to  weather  modification   399 

General  discussion   399 

Opposition  to  the  seeding  project  above  Hungry  Horse  Dam.  399 

Tri-State  Natural  Weather  Association   400 

Citizens  for  the  Preservation  of  Natural  Resources   402 

Chapter  9 

Foreign'activities  in  weather  modification   405 

Introduction   405 

World  Meteorological  Organization  register  of  weather  modification 

projects   408 

Description  of  weather  modification  activities  in  some  foreign  nations.  412 

The  Union  of  Soviet  Socialist  Republics   412 

Overview  of  projects  in  the  U.S.S.R   412 

Summary  of  weather  modification  and  related  atmospheric 

research  in  the  U.S.S.R   413 

Israel   415 

Australia   416 

Canada   418 

Mexico   419 

People's  Republic  of  China   420 

Kenya   421 

Republic  of  South  Africa   422 

Rhodesia   423 

India   423 

The  Swiss  hail  experiment   424 

Chapter  10 

International  aspects  of  weather  modification   427 

Introduction   427 

Convention  on  the  prohibition  of  military  or  any  other  hostile  use  of 

environmental  modification  techniques   429 

Development  of  the  treaty   429 

Criticism  of  the  convention   431 

Activities  since  the  United  Nations  approval  of  the  convention..  432 
Activities  of  the  World  Meteorological  Organization  in  weather 

modification   433 

Precipitation  enhancement  program  (PEP)   434 

Other  WMO  activities  in  weather  modification   436 

Registration  and  reporting  of  weather  modification  projects.  436 

WMO  conferences  on  weather  modification   436 

Typhoon  and  serious  storm  modification   437 

Global  atmospheric  research  programme   437 

Legal  aspects  of  weather  modification   437 

United  Nations  Conference  on  the  Human  Environment   438 

Declaration  of  the  United  Nations  Conference  on  the  Human 

Environment   438 

Action  Plan  for  the  Human  Environment   438 

Earthwatch  Program   439 

Study  of  Man's  Impact  on  Climate   439 

Other  international  activities   440 

United  States/Canadian  agreement   440 

North  American  Interstate  Weather  Modification  Council   440 

Congressional  activities   441 

Weather  modification  as  a  weapon  of  war   441 

Senate  Resolution  71,  prohibiting  environmental  modification 

as  a  weapon  of  war   441 

Congressional  activities  related  to  hostile  use  of  weather 

modification,  1974-76   442 

Other  Congressional  actions  relating  to  weather  modification   443 

Senate  Concurrent  Resolution  67 — U.S.  participation  in  the 

world  weather  program   443 

National  Weather  Modification  Policy  Act  of  1976   444 

Senate  Resolution  49   444 



U.S.  foreign  policy   444 

Various  executive  branch  proposals   445 

National  Advisory  Committee  on  Oceans  and  Atmosphere   447 

Activities  in  1977   448 

Chapter  11 

Legal  aspects  of  weather  modification   449 

Domestic   449 

Private  rights  in  the  clouds   449 

Liability  for  weather  modification   453 

Defenses  which  may  be  raised  against  claims  of  liability   456 

Interstate  allocation  of  atmospheric  water   457 

Methods  of  controlling  weather  modification   459 

Congressional  authority  under  the  Constitution  to  regulate  or 

license  weather  modification  activities   461 

Federalism   461 

The  commerce  clause   461 

The  commerce  clause  generally   462 

The  commerce  clause  and  the  regulation  of  navigable 

waters   463 

Limitations  on  the  commerce  power   464 

Fiscal  powers   465 

War  powers   466 

Property  power   466 

Treaty  power   467 

Conclusion   467 

International   468 

Certain  hostile  uses  of  weather  modification  are  prohibited   471 

Nations  are  responsible  for  environmental  conduct  which  causes 

injury  or  damage  in  or  to  other  nations   471 

Nations  are  liable  for  injuries  sustained  by  aliens  within  their 
territory  caused  by  tortuous  conduct  in  violation  of  inter- 
national law   472 

Nations  or  their  citizens  may  be  liable  for  injury  and  damage 
they  caused  to  citizens  of  another  nation  occurring  in  that 

nation   472 

Chapter  12 

Economic  aspects  of  weather  modification   475 

Introduction   475 

Economic  setting   476 

Economic  aspects  of  weather  modification  procedures   477 

Fog  dispersal   477 

Precipitation  augmentation   478 

Orographic  cloud  seeding   478 

Convective  cloud  seeding   478 

Precipitation  augmentation  and  energy  considerations   479 

Hail  suppression   480 

Lightning  suppression  and  reduction  in  storm  damage   480 

Analytic  methods  for  economic  analysis   481 

Case  studies  of  the  economics  of  weather  modification   482 

Hungry  Horse  Area,  Montana   482 

Connecticut  River  basin   483 

State  of  Illinois   483 

Nine-county  Southeastern  Crop  Reporting  District,  South  Dakota,  483 

Colorado  River   484 

Conclusions   486 

Chapter  13 

Ecological  effects  of  weather  modification   487 

Introduction   487 

Modification  of  weather  and  climate   487 

Ecology  and  ecological  systems  —  487 

Knowledge  of  ecological  implications  of  applied  weather  modifi- 
cation technologies   488 



Important  variables   490 

Temporal  considerations   491 

Season  of  modification  effort   491 

Duration  of  effort:  Short-  v.  long-term   491 

Regularity  of  modification  effort   491 

Ecosystem  type   492 

Aquatic  v.  terrestrial  systems   492 

Cultivated  v.  natural  systems   492 

Arid  v.  humid  systems   492 

Cumulative  and  synergistic  effects   492 

Effects  of  silver  iodide*   493 

Deliberate  weather  modification   496 

Precipitation  enhancement   496 

Increased  rainfall   496 

Snowpack  augmentation   497 

Severe  storm  abatement   498 

Fog  dispersal   499 

Hail  suppression   499 

Alteration  or  arrest  of  lightning  discharges   499 

Inadvertent  weather  modification   499 

Extra-area  effects   499 

Long-term,  climatic,  and  global  implications   500 

Summary  and  conclusions   501 


A.  Statement   on  weather  modification    in   Congressional   Record  of 

June  17,  1975,  by  Congressman  Gilbert  Gude,  containing  White 

House  statement  on  Federal  weather  modification  policy   503 

B.  Department  of  Defense  statement  on  position  on  weather  modification.  509 

C.  Text  of  United  Nations  Convention  on  the  prohibition  of  military 

or  any  other  hostile  use  of  environmental  modification  techniques   510 

D.  State  statutes  concerning  weather  modification   514 

Arizona   515 

California   516 

Colorado   520 

Connecticut   528 

Florida   529 

Hawaii   531 

Idaho   531 

Illinois   533 

Iowa   541 

Kansas   543 

Louisiana   549 

Minnesota   550 

Montana   554 

Nebraska   557 

Nevada   565 

New  Hampshire   571 

New  Mexico   571 

New  York   573 

North  Dakota   573 

Oklahoma   584 

Oregon   59 1 

Pennsylvania   599 

South*  Dakota   604 

Texas   600 

Utah   612 

Washington   613 

West  Virginia   618 

Wisconsin   622 

Wyoming   622 

E.  List  of  State  contacts  for  further  information  on  weather  modification 

activities  within  the  States   625 

F.  Agreement   on   exchange  of   information   on   weather  modification 

between  the  United  States  of  America  and  Canada   627 


G.  Weather  modification  activities  in  the  United  States  during  calendar  Pa?e 

year  1975   630 

H.  Selected  bibliography  of  publications  in  weather  modification   641 

I.  Public  laws  dealing  specifically  with  weather  modification   640 

J.    Summary  of  language  in  congressional  documents  supporting  public 

works  appropriations  for  the  Bureau  of  Reclamation's  atmospheric 

water  resources  program   655 

K.  Membership  and  charter  of  the  U.S.   Department  of  Commerce 

Weather  Modification  Advisory  Board   660 

L.  Rules  and  regulations  and  required  forms  for  submitting  information 
on  weather  modification  activities  to  the  National  Oceanic  and 
Atmospheric  Administration,  U.S.  Department  of  Commerce,  in 

accordance  with  requirements  of  Public  Law  92-205   662 

M.  Selected  State  rules  and  regulations  for  the  administration  of  State 

weather  modification  statutes   676 

Illinois   676 

Kansas   6  S3 

North  Dakota   691 

Utah   707 

Washington   712 

N.  Documents  of  the  Weather  Modification  Association   717 

O.   Policy  statement  of  the  American  Meteorological  Society  on  purposeful 

and  inadvertent  modification  of  weather  and  climate   722 

P.  Reporting  agencies  of  member  countries  and  questionnaire  circulated 
to  receive  weather  modification  information  from  members  of  the 

World  Meteorological  Organization   724 

Q.  Report  of  the  World  Meteorological  Organization/ United  Nations 
Environment  programme  informal  meeting  on  legal  aspects  of 

weather  modification   727 

R.  Text  of  Senate  Resolution  71;  considered,  amended,  and  agreed  to 

July  11,  1973   734 

S.    Reported  cases  on  weather  modification   740 

T.    Glossary  of  selected  terms  in  weather  modification   741 

34-857—79  2 


Weather  modification  is  generally  considered  to  be  the  deliberate 
effort  to  improve  atmospheric  conditions  for  beneficial  human  pur- 
poses— to  augment  water  supplies  through  enhanced  precipitation  or 
to  reduce  economic  losses,  property  damages,  and  deaths  through 
mitigation  of  adverse  effects  of  hail,  lightning,  fog,  and  severe  storms. 
Not  all  weather  modification  activities,  however,  have  been  or  can  be 
designed  to  benefit  everyone,  and  some  intentional  operations  have 
been  used,  or  are  perceived  to  have  been  used,  as  a  weapon  of  war 
to  impede  the  mobility  or  tactical  readiness  of  an  enemy.  Further- 
more, environmental  change  is  also  effected  unintentionally  and  with- 
out any  purpose  at  all,  as  man  inadvertently  modifies  the  weather  and 
climate,  whether  for  better  or  worse  scientists  are  not  certain,  through 
activities  such  as  clearing  large  tracts  of  land,  building  urban  areas, 
and  combustion  of  fossil  fuels. 

Historically,  there  have  been  attempts,  often  nonscientific  or  pseudo- 
scientific  at  best,  to  change  the  weather  for  man's  benefit.  Until  the 
20th  century,  however,  the  scientific  basis  for  such  activities  was 
meager,  with  most  of  our  current  understanding  of  cloud  physics  and 
precipitation  processes  beginning  to  unfold  during  the  1930's.  The 
modern  period  in  weather  modification  is  about  three  decades  old,  dat- 
ing from  events  in  1946,  when  Schaefer  and  Langmuir  of  the  General 
Electric  Co.  demonstrated  that  a  cloud  of  supercooled  water  droplets 
could  be  transformed  into  ice  crystals  when  seeded  with  dry  ice.  Soon 
afterward  it  was  discovered  that  fine  particles  of  pure  silver  iodide, 
with  crystal  structure  similar  to  that  of  ice,  were  effective  artificial 
ice  nuclei,  and  that  seeding  clouds  with  such  particles  could  produce 
ice  crystals  at  temperatures  just  below  freezing.  Silver  iodide  remains 
the  most  often  used  material  in  modern  "cloud  seeding." 

By  the  1950's,  many  experimental  and  operational  weather  modifi- 
cation projects  were  underway;  however,  these  early  attempts  to 
augment  precipitation  or  to  alter  severe  storm  effects  were  often  in- 
conclusive or  ineffective,  owing  to  improper  experimental  design,  lack 
of  evaluation  schemes,  and  the  primitive  state  of  the  technology. 
Through  research  programs  over  the  past  two  decades,  including 
laboratory  studies  and  field  experiments,  understanding  of  atmos- 
pheric processes  essential  to  improved  weather  modification  tech- 
nology has  been  advanced.  Sophisticated  evaluation  schemes  have  been 
developed,  using  elaborate  statistical  tools;  there  has  also  been  im- 
provement in  measuring  instruments  and  weather  radar  systems ;  and 
simulation  of  weather  processes  using  numerical  models  and  high 
speed  computers  has  provided  further  insights.  Meanwhile,  commer- 
cial weather  modifiers,  whose  number  decreased  dramatically  along 
with  the  total  area  of  the  United  States  covered  by  their  operations 
after  the  initial  surge  of  the  1950  era,  have  grown  in  respectability  and 
competence,  and  their  operations  have  incorporated  improvements  as 
they  benefited  from  their  accumulated  experience  and  from  the  re- 



suits  of  research  projects.  Since  such  operations  are  designed  for  prac- 
tical results,  such  as  increased  precipitation  or  reduced  hail,  however, 
the  sophisticated  evaluation  procedures  now  used  in  most  research 
projects  are  most  often  not  used,  so  that  the  effectiveness  of  the  opera- 
tions is  frequently  difficult  to  assess. 

Weather  modification  is  at  best  an  emerging  technology.  Progress  in 
development  of  the  technology  over  the  past  30  years  has  been  slow, 
although  there  has  been  an  increased  awareness  of  the  complex  nature 
of  atmospheric  processes  and  a  steady  improvement  in  basic  under- 
standing of  those  processes  which  underlie  attempts  at  deliberate  modi- 
fication of  weather  phenomena.  Though  most  cloud-seeding  practices 
are  based  on  a  common  theory  and  form  the  basis  for  a  number  of  seed- 
ing objectives,  there  are  really  a  series  of  weather  modification 
technologies,  each  tailored  to  altering  a  particular  atmospheric  pheno- 
menon and  each  having  reached  a  different  state  of  development  and 
operational  usefulness.  For  example,  cold  fog  clearing  is  now  consid- 
ered to  be  operational,  while,  at  the  other  extreme,  the  abatement  of 
severe  storms  such  as  hurricanes  remains  in  the  initial  research  phase. 
Development  progress  for  each  of  these  technologies  appears  to  be 
much  less  a  function  of  research  effort  expended  than  a  dependence  on 
the  fundamental  atmospheric  processes  and  the  ease  by  which  they  can 
be  altered.  There  continues  to  be  obvious  need  for  further  research  and 
development  to  refine  those  few  techniques  for  which  there  has  been 
some  success  and  to  advance  technology  where  progress  has  been  slow 
or  at  a  virtual  standstill. 

The  following  summary  provides  a  reasonably  accurate  assessment 
of  the  current  status  of  weather  modification  technology : 

1.  The  only  routine  operational  projects  are  for  clearing  cold  fog. 
Research  on  warm  fog  has  yielded  some  useful  knowledge  and  good 
models,  but  the  resulting  technologies  are  so  costly  that  they  are  usable 
mainly  for  military  purposes  and  very  busy  airports. 

2.  Several  longrunning  efforts  to  increase  winter  snowpack  by  seed- 
ing clouds  in  the  mountains  suggest  that  precipitation  can  be  increased 
by  some  15  percent  over  what  would  have  happened  "naturally." 

3.  A  decade  and  a  half  of  experience  with  seeding  winter  clouds  on 
the  U.S.  west  coast  and  in  Israel,  and  summer  clouds  in  Florida,  also 
suggest  a  10-  to  15-percent  increase  over  "natural"  rainfall.  Hypotheses 
and  techniques  from  the  work  in  one  area  are  not  directly  transferable 
to  other  areas,  but  will  be  helpful  in  designing  comparable  experiments 
with  broadly  similar  cloud  systems. 

4.  Numerous  efforts  to  increase  rain  by  seeding  summer  clouds  in  the 
central  and  western  parts  of  the  United  States  have  left  many  questions 
unanswered.  A  major  experiment  to  try  to  answer  them — for  the  High 
Plains  area — is  now  in  its  early  stages. 

5.  It  is  scientifically  possible  to  open  holes  in  wintertime  cloud  layers 
by  seeding  them.  Increasing  sunshine  and  decreasing  energy  consmp- 
tion  may  be  especially  relevant  in  the  northeastern  quadrant  of  the 
United  States. 

0.  Some  $10  million  is  spent  by  private  and  local  public  sponsors  for 
cloud-seeding  efforts,  but  these  projects  arc  not  designed  as  scientific 
experiments  and  it  is  difficult  to  say  for  sure  that  operational  cloud 
seeding  causes  the  claimed  results. 


7.  Knowledge  about  hurricanes  is  improving  with  good  models  of 
their  behavior.  But  the  experience  in  modifying  that  behavior  is  primi- 
tive so  far.  It  is  inherently  difficult  to  find  enough  test  cases,  especially 
since  experimentation  on  typhoons  in  the  Western  Pacific  has  been 
blocked  for  the  time  being  by  international  political  objections. 

8.  Although  the  Soviets  and  some  U.S.  private  operators  claim  some 
success  in  suppressing  hail  by  seeding  clouds,  our  understanding  of  the 
physical  processes  that  create  hail  is  still  weak.  The  one  major  U.S. 
held  experiment  increased  our  understanding  of  severe  storms,  but 
otherwise  proved  mostly  the  dimensions  of  what  we  do  not  yet  know. 

9.  There  have  been  many  efforts  to  suppress  lightning  by  seeding 
thunderstorms.  Our  knowledge  of  the  processes  involved  is  fair,  but  the 
technology  is  still  far  from  demonstrated,  and  the  U.S.  Forest  Service 
has  recently  abandoned  further  lightning  experiments.1 

Modification  processes  may  also  be  initiated  or  triggered  inadvert- 
ently rather  than  purposefully,  and  the  possibility  exists  that  society 
may  be  changing  the  climate  through  its  own  actions  by  pushing  on 
ceitain  leverage  points.  Inadvertently,  man  is  already  causing  measur- 
able variations  on  the  local  scale.  Artificial  climatic  effects  have  been 
observed  and  documented  on  local  and  regional  scales,  particularly  in 
and  downwind  of  heavily  populated  industrial  areas  where  waste  heat, 
particulate  pollution  and  altered  ground  surface  characteristics  are 
primarily  responsible  for  the  perceived  climate  modification.  The  cli- 
mate in  and  near  large  cities,  for  example,  is  warmer,  the  daily  range 
of  temperature  is  less,  and  annual  precipitation  is  greater  than  if  the 
cities  had  neA^er  been  built.  Although  not  verifiable  at  present,  the  time 
may  not  be  far  off  when  human  activities  will  result  in  measurable 
large-scale  changes  in  weather  and  climate  of  more  than  passing  sig- 
nificance. It  is  important  to  appreciate  the  fact  that  the  role  of  man  at 
this  global  level  is  still  controversial,  and  existing  models  of  the  gen- 
eral circulation  are  not  yet  capable  of  testing  the  effects  in  a  conclusive 

Nevertheless,  a  growing  fraction  of  current  evidence  does  point  to 
the  possibility  of  unprecedented  impact  on  the  global  climate  by  hu- 
man activities,  albeit  the  effects  may  be  occurring  below  the  threshold 
where  they  could  be  statistically  detected  relative  to  the  record  of  nat- 
ural fluctuations  and.  therefore,  could  be  almost  imperceptible  amid 
the  ubiquitous  variability  of  climate.  But  while  the  degree  of  influence 
on  world  climate  may  as  yet  be  too  small  to  detect  against  the  back- 
ground of  natural  variations  and  although  mathematical  models  of 
climatic  change  are  still  imperfect,  significant  global  effects  in  the 
future  are  inferred  if  the  rates  of  growth  of  industry  and  population 

For  over  30  years  both  legislative  and  executive  branches  of  the 
Federal  Government  have  been  involved  in  a  number  of  aspects  of 
weather  modification.  Since  1947  about  110  weather  modification  bills 
pertaining  to  research  support,  operations,  grants,  policy  studies,  regu- 
lations, liabilities,  activity  reporting,  establishment  of  panels  and  com- 
mittees, and  international  concerns  have  been  introduced  in  the  Con- 

1  Weather  Modification  Advisory  Board.  "A  U.S.  Policy  to  Enhance  the  Atmospheric 
Environment,"  Oct.  21,  1977.  In  testimony  by  Harlan  Cleveland.  Weather  modification. 
Hearing  before  the  Subcommittee  on  the  Environment  and  the  Atmosphere,  Committee  on 
Science  and  Technology.  U.S.  House  of  Representatives.  93th  Cong.,  1st  sess.,  Oct.  26, 
1977,  Washington,  U.S.  Government  Printing  Office,  1977.  pp.  28-30. 


gress.  Resolutions,  mostly  concerned  with  using  weather  modification 
ns  a  weapon  and  promotion  of  a  United  Nations  treaty  banning  such 
activities,  have  also  been  introduced  in  both  houses  of  the  Congress ; 
one  such  resolution  was  passed  by  the  Senate. 

Six  public  laws  specifically  dealing  with  weather  modification  have 
been  enacted  since  1953,  and  others  have  included  provisions  which  are 
in  some  way  relevant  to  weather  modification.  Federal  weather  modi- 
fication legislation  has  dealt  primarily  with  three  aspects — research 
program  authorization  and  direction,  collection  and  reporting  of  in- 
formation on  weather  modification  activities,  and  the  commissioning 
of  major  policy  studies.  In  addition  to  direction  through  authorizing 
legislation,  the  Congress  initiated  one  major  Federal  research  pro- 
gram through  a  write-in  to  an  appropriations  bill;  this  program 
regularly  receives  support  through  additional  appropriations  beyond 
recommended  OMB  funding  levels. 

There  are  two  Federal  laws  currently  in  effect  which  are  specifically 
concerned  with  weather  modification.  Public  Law  92-205,  of  Decem- 
ber 18,  1971,  and  its  amendments  requires  the  reporting  of  all  non- 
Federal  activities  to  the  Secretary  of  Commerce  and  publication  "from 
time  to  time"  of  summaries  of  such  activities  by  the  Secretary  of 
Commerce.2  The  National  Weather  Modification  Policy  Act  of  1976 
(Public  Law  94-490),  enacted  October  13, 1976,  directed  the  Secretary 
of  Commerce  to  conduct  a  major  study  on  weather  modification  and  to 
submit  a  report  containing  a  recommended  Federal  policy  and  Fed- 
eral research  program  on  wTeather  modification.  The  Secretary  ap- 
pointed a  non-Government  Weather  Modification  Advisory  Board  to 
conduct  the  mandated  study,  the  report  on  which  is  to  be  submitted 
to  the  Secretary  for  her  review  and  comment  and  subsequent  trans- 
mittal to  the  President  and  the  Congress  during  1978.  It  is  expected 
that,  following  receipt  of  the  aforementioned  report,  the  Congress  will 
consider  legislation  on  Federal  weather  modification  policy,  presuma- 
bly during  the  96th  Congress. 

Congressional  interest  in  weather  modification  has  also  been  mani- 
fested in  a  number  of  hearings  on  various  bills,  in  oversight  hearings 
on  pertinent  ongoing  Federal  agency  programs,  in  consideration  of 
some  22  resolutions  having  to  do  with  weather  modification,  and  in 
commissioning  studies  on  the  subject  by  congressional  support 

The  principal  involvement  in  weather  modification  of  the  Federal 
Government  has  been  through  the  research  and  development  programs 
of  the  several  Federal  departments  and  agencies.  Although  Federal 
research  programs  can  be  traced  from  at  least  the  period  of  World 
War  II,  the  programs  of  most  agencies  other  than  the  Defense  Depart- 
ment were  not  begun  until  the  1950's  and  1960's.  These  research  and 
development  programs  have  been  sponsored  at  various  times  by  at 
least  eight  departments  and  independent  agencies — including  the  De- 
partments of  Agriculture,  Commerce,  Defense,  Energy,  Interior,  and 
Transportation,  the  National  Aeronautics  and  Space  Administration 
(NASA),  and  the  National  Science  Foundation  (NSF).  In  fiscal  year 

2  Although  Federal  agencies  were  excluded  from  the  requirements  of  this  not.  upon  agreement,  the  agencies  also  submit  information  on  their  weather  mollification 
projects  to  tlie  Secretary  of  Commerce,  so  that  there  is  a  single  repository  for  information 
on  nil  weather  modification  activities  conducted  within  the  United  States. 


1978  six  agency  programs  were  reported,  those  of  Transportation  and 
NASA  having  been  phased  out,  while  that  of  Agriculture  was  severely 

Total  funding  for  Federal  weather  modification  research  in  fiscal 
year  1978  is  estimated  at  about  $17  million,  a  decline  from  the  highest 
funding  level  of  $20  million  reached  in  fiscal  year  1976.  The  largest 
programs  are  those  of  the  Departments  of  Interior  and  Commerce  and 
of  the  NSF.  The  NSF  has  supported  weather  modification  research 
over  a  broad  spectrum  for  two  decades,  although  its  fiscal  year  1978 
funding  was  reduced  by  more  than  50  percent,  and  it  is  not  clear  that 
more  than  the  very  basic  atmospheric  science  supportive  of  weather 
modification  will  be  sponsored  hereafter  by  the  Foundation. 

The  present  structure  of  Federal  organization  for  weather  modifi- 
cation research  activities  is  characterized  essentially  by  the  mission- 
oriented  approach,  whereby  each  of  the  agencies  conducts  its  own 
program  in  accordance  with  broad  agency  goals  or  under  specific  direc- 
tions from  the  Congress  or  the  Executive.  Programs  have  been  loosely 
coordinated  through  various  independent  arrangements  and/or  advi- 
sory panels  and  particularly  through  the  Interdepartmental  Commit- 
tee for  Atmospheric  Sciences  (ICAS).  The  ICAS,  established  in  1959 
by  the  former  Federal  Council  for  Science  and  Technology,  provides 
advice  on  matters  related  to  atmospheric  science  in  general  and  has 
also  been  the  principal  coordinating  mechanism  for  Federal  research 
in  weather  modification. 

In  1958  the  National  Science  Foundation  was  designated  lead  agency 
for  Federal  weather  modification  research  by  Public  Law  85-510,  a 
role  which  it  maintained  until  1968,  when  Public  Law  90-407  removed 
this  responsibility  from  NSF.  No  further  action  was  taken  to  name  a 
lead  agency,  although  there  have  been  numerous  recommendations  to 
designate  such  a  lead  agency,  and  several  bills  introduced  in  the  Con- 
gress would  have  named  either  the  Department  of  the  Interior  or  the 
Department  of  Commerce  in  that  role.  During  the  10-year  period  from 
1958  to  1968  the  NSF  promoted  a  vigorous  research  program  through 
grants  to  various  research  organizations,  established  an  Advisory 
Panel  for  Weather  Modification,  and  published  a  series  of  10  annual 
reports  on  weather  modification  activities  in  the  United  States.  Since 
1968  there  has  been  a  lapse  in  Federal  weather  modification  policy  and 
in  the  Federal  structure  for  research  programs,  although,  after  a 
hiatus  of  over  3  years,  the  responsibility  for  collecting  and  disseminat- 
ing information  on  weather  modification  activities  was  assigned  to  the 
Commerce  Department  in  1971.  An  important  consideration  of  any 
future  weather  modification  legislation  will  probably  be  the  organiza- 
tional structure  of  the  Federal  research  program  and  that  for  admin- 
istration of  other  related  functions  which  may  be  the  responsibility  of 
the  Federal  Government.  Options  include  a  continuation  of  the  present 
mission-oriented  approach  with  coordination  through  the  ICAS  or  a 
similar  interagency  body,  redesignation  of  a  lead  agency  with  some 
autonomy  remaining  with  the  several  agencies,  or  creation  of  a  single 
agency  with  control  of  all  funding  and  all  research  responsibilities. 
The  latter  could  be  an  independent  agency  or  part  of  a  larger  depart- 
ment ;  it  would  presumably  also  administer  other  aspects  of  Federal 
weather  modification  responsibilities,  such  as  reporting  of  activities, 


regulation  and  licensing,  and  monitoring  and  evaluation  of  operations, 
if  a  n}'  or  all  of  these  functions  should  become  or  continue  to  be  services 
performed  at  the  Federal  level. 

In  addition  to  specific  research  programs  sponsored  bv  Federal  agen- 
cies, there  are  other  functions  related  to  weather  modification  which 
are  performed  in  several  places  in  the  executive  branch.  Various  Fed- 
eral advisory  panels  and  committees  and  their  staffs — established  to 
conduct  in-depth  studies  and  prepare  comprehensive  reports,  to  pro- 
vide advice  and  recommendations,  or  to  coordinate  Federal  weather 
modification  programs — have  been  housed  and  supported  within  exec- 
utive departments,  agencies,  or  offices.  The  program  whereby  Federal 
and  non-Federal  U.S.  weather  modification  activities  are  reported  to 
the  Government  is  administered  by  the  National  Oceanic  and  Atmos- 
pheric Administration  (NOAA)  within  the  Commerce  Department. 
The  State  Department  negotiates  agreements  with  other  nations  which 
might  be  affected  by  U.S.  experiments  and  has  arranged  for  Federal 
agencies  and  other  U.S.  investigators  to  participate  in  international 
meteorological  projects,  including  those  in  weather  modification.  In 
the  United  Nations,  the  United  States  has  been  active  in  promoting  the 
adoption  of  a  treaty  banning  weather  modification  as  a  military 

In  accordance  with  the  mandates  of  several  public  laws  or  self-ini- 
tiated bv  the  agencies  or  interagency  committees,  the  executive  branch 
of  the  Federal  Government  has  undertaken  a  number  of  major  weather 
modification  policy  studies  over  the  past  25  years.  Each  of  the  com- 
pleted major  studies  was  followed  by  a  report  which  included  findings 
and  recommendations.  The  most  recent  study  is  the  one  noted  earlier 
that  is  being  conducted  by  the  Weather  Modification  Advisory  Board 
on  behalf  of  the  Secretarv  of  Commerce,  pursuant  to  requirements  of 
the  National  Weather  Modification  Policy  Act  of  1976.  Nearly  all 
previous  studies  emphasized  the  needs  for  designation  of  a  lead  agency, 
increased  basic  meteorological  research,  increased  funding,  improve- 
ment of  support  and  cooperation  from  agencies,  and  consideration  of 
legal,  socioeconomic,  environmental,  and  international  aspects.  Other 
recommendations  have  included  improvement  of  program  evaluation, 
studv  of  inadvertent  effects,  increased  regulation  of  activities,  and  a 
number  of  specific  research  projects.  Although  some  of  the  recom- 
mended activities  have  been  undertaken,  many  have  not  resulted  in 
specific  actions  to  date.  Almost  invariably  it  was  pointed  out  in  the 
studies  that  considerable  progress  would  result  from  increased  fund- 
ing. Although  funding  for  weather  modification  research  has  increased 
over  t  he  past  20  years,  most  funding  recommendations  have  been  for 
considerably  higher  levels  than  those  provided.  Since  fiscal  year  1976, 
the  total  Federal  research  funding  for  weather  modification  research 
hn=.  in  fact,  decreased. 

Most  States  in  the  Nation  have  some  official  interest  in  weather 
modification  ;  29  of  them  have  some  form  of  law  which  relates  to  such 
activities,  usually  concerned  with  various  facets  of  regulation  or  con- 
trol of  operations  within  the  Slate  and  sometimes  pertaining  to  au- 
thorization for  funding  research  and/or  operations  at  the  State  or 
local  level.  A  State's  weather  modification  law  usually  reflects  its  gen- 
eral policy  toward  weather  modification;  some  State  laws  tend  to  en- 


courage  development  and  use  of  the  technology,  while  others  dis- 
courage such  activities. 

The  current  legal  regime  regulating  weather  modification  has  been 
developed  by  the  States  rather  than  the  Federal  Government,  except 
in  the  areas  of  research  support,  commissioning  studies,  and  requiring 
reporting  of  activities.  The  various  regulatory  and  management  func- 
tions which  the  States  perform  include:  (1)  issuance,  renewal,  sus- 
pension, and  revocation  of  licenses  and  permits;  (2)  monitoring  and 
collecting  of  information  on  activities  through  requirements  to  main- 
tain records,  submission  of  periodic  activity  reports,  and  inspection 
of  premises  and  equipment;  (3)  funding  and  managing  of  State  or 
locally  organized  operational  and/or  research  programs ;  (4)  evalua- 
tion and  advisory  services  to  locally  organized  public  and  private  op- 
erational programs  within  the  State;  and  (5)  miscellaneous  admin- 
istrative activities,  including  the  organization  and  operation  of  State 
agencies  and  boards  which  are  charged  with  carrying  out  statutory 
responsibilities.  Administration  of  the  regulatory  and  managerial  re- 
sponsibilities pertaining  to  weather  modification  within  the  States  is 
accomplished  through  an  assortment  of  institutional  structures,  in- 
cluding departments  of  water  or  natural  resources,  commissions,  and 
special  governing  or  advisory  groups.  Often  there  is  a  combination  of 
two  or  more  of  these  agencies  or  groups  in  a  State,  separating  func- 
tions of  pure  administration  from  those  of  appeals,  permitting,  or  ad- 
visory services. 

Involvement  in  weather  modification  operational  and  research  pro- 
grams varies  from  State  to  State.  Some  support  research  only,  while 
others  fund  and  operate  both  research  and  operational  programs.  In 
some  cases  funding  only  is  provided  to  localities,  usually  at  the  county 
level,  where  operational  programs  have  been  established.  The  recent 
1976-77  drought  led  some  Western  States  to  initiate  emergency  cloud- 
seeding  programs  as  one  means  of  augmenting  diminishing  water  sup- 
plies. Research  conducted  by  atmospheric  and  other  scientists  at  State 
universities  or  other  research  agencies  may  be  supported  in  part  with 
State  funds  but  is  often  funded  by  one  of  the  major  Federal  weather 
modification  programs,  such  as  that  of  the  Bureau  of  Reclamation  or 
the  National  Science  Foundation.  In  a  few  cases.  States  contribute 
funds  to  a  Federal  research  project  which  is  conducted  jointly  with 
the  States  and  partly  within  their  borders. 

In  1975,  1976,  and  1977,  respectively,  there  were  58,  61,  and  88  non- 
federally  supported  weather  modification  projects,  nearly  all  opera- 
tional, conducted  throughout  the  United  States.  These  projects  were 
sponsored  by  community  associations,  airlines,  utilities,  private  in- 
terests, municipal  districts,  cities,  and  States.  Eighty-five  percent  of 
all  projects  in  the  United  States  during  1975  were  carried  out  west  of 
Kansas  City,  with  the  largest  number  in  California.  In  that  State 
there  were  11  proipets  in  each  of  the  vears  1975  and  1976,  and  20 
projects  during  1977.  The  majority  of  these  operational  projects  were 
designed  to  increase  precipitation;  others  were  intended  for  sup- 
pression of  hail  or  dispersal  of  fogs,  the  latter  principally  at  airports. 

In  most  instances,  the  principal  beneficiaries  of  weather  modification 
are  the  local  or  regional  users,  who  include  farmers  and  ranchers, 
weather-related  industries,  municipalities,  airports,  and  utilities — 


those  individuals  and  groups  whose  economic  well-being  and  whose 
lives  and  property  are  directly  subject  to  adverse  consequences  of 
drought  or  other  severe  weather.  It  is  at  the  local  level  where  the  need 
to  engage  in  weather  modification  is  most  keenly  perceived  and  also 
where  possible  negative  effects  from  such  activities  are  most  apparent 
to  some  sectors  of  the  population.  It  follows  that  both  the  greatest  sup- 
port and  the  strongest  opposition  to  weather  modification  projects  are 
focussed  at  the  local  level.  The  popularity  of  a  particular  project  and 
the  degree  of  controversy  surrounding  it  are  frequently  determined  by 
the  extent  to  which  local  citizens  and  local  organizations  have  had  a 
voice  in  the  control  or  funding  of  the  project.  At  the  local  level,  deci- 
sions to  implement  or  to  withdraw  from  a  project  can  most  often  be 
made  with  minimum  social  stress.  Indeed,  studies  have  shown  that  most 
people  are  of  the  opinion  that  local  residents  or  local  government  offi- 
cials should  make  decisions  on  whether  or  not  to  use  weather  modifica- 
tion technology  in  a  given  situation. 

Many  of  the  operational  weather  modification  services  provided  for 
private  groups  and  governmental  bodies  within  the  States  are  carried 
out  under  contract  by  commercial  firms  who  have  developed  expertise 
in  a  broad  range  of  capabilities  or  who  specialize  in  particular  services 
essential  to  both  operational  or  research  projects.  Contracts  may  cover 
only  one  season  of  the  year,  but  a  number  of  them  are  renewed  an- 
nually, with  target  areas  ranging  from  a  few  hundred  to  a  few  thou- 
sand square  miles.  In  197G,  6  of  the  10  major  companies  having 
substantial  numbers  of  contracts  received  about  $2.7  million  for  op- 
erations in  the  United  States,  and  a  few  of  these  companies  also  had 
contracts  overseas.  Owing  to  increased  demand  for  emergency  pro- 
grams during  the  recent  drought,  it  is  estimated  that  1977  contracts 
totaled  about  $3.5  million. 

The  initial  role  of  the  private  weather  modification  operators  was  to 
sustain  activities  during  the  early  years,  when  there  was  often  heated 
scientific  controversy  with  other  meteorologists  over  the  efficacy  of 
cloud  seeding.  Later,  their  operations  provided  a  valuable  data  base 
which  permitted  the  early  evaluation  of  seeding  efforts  and  estimates 
of  potential  prospects  for  the  technology,  meanwhile  growing  in  com- 
petence and  public  respect.  Today,  more  often  than  not,  they  work 
hand  in  hand  with  researchers  and,  in  fact,  they  often  participate  in 
research  projects,  contributing  much  of  their  knowhow  acquired 
through  their  unique  experiences. 

Important  among  private  institutions  concerned  with  weather  modi- 
fication are  the  professional  organizations  of  which  research  and  op- 
erational weather  modifiers  and  other  interested  meteorologists  are 
members.  These  include  the  American  Meteorological  Society,  the 
Weather  Modifical ion  Association,  and  the  Irrigation  and  Drainage 
Division  of  the  American  Society  of  Civil  Engineers.  Through  the 
meetings  and  publications  of  these  organizations  the  scientific,  tech- 
nical, and  legal  problems  and  findings  on  weather  modification  are 
aired  and  discussed.  These  groups  also  address  other  matters  such  as 
statements  of  weather  modification  policy,  opinions  on  pending  legis- 
lation, social  implieations.  and  professional  standards  and  certifica- 
tion. Tn  addition,  the  North  American  Interstate  Weather  Modifica- 
tion Council  is  an  organizai  ion  whose  membership  consists  of  govern- 


ments  of  U.S.  States  and  Canadian  Provinces  and  the  Government  of 
Mexico,  which  serves  as  a  forum  for  interstate  coordination  and  ex- 
change of  information  on  weather  modification. 

Weather  modification  is  often  controversial,  and  both  formal  and 
informal  opposition  groups  have  been  organized  in  various  sections 
of  the  country.  Reasons  for  such  opposition  are  varied  and  are  based 
on  both  real  and  perceived  adverse  consequences  from  weather  modifi- 
cation. Sometimes  with  little  or  no  rational  basis  there  are  charges 
by  these  groups  that  otherwise  unexplained  and  usually  unpleasant 
weather- related  events  are  linked  to  cloud  seeding.  There  are  also  cases 
where  some  farmers  are  economically  disadvantaged  through  receiving 
more,  or  less  than  optimum  rainfall  for  their  particular  crops,  when 
artificial  inducement  of  such  conditions  may  have  indeed  been  planned 
to  benefit  those  growing  different  crops  with  different  moisture  re- 
quirements. Opposition  groups  are  often  formed  to  protect  the  legiti- 
mate rights  of  farmers  under  such  circumstances. 

While  the  United  States  is  the  apparent  leader  in  weather  modifi- 
cation research  and  operations,  other  countries  have  also  been  active. 
Information  on  foreign  weather  modification  activities  is  not  uni- 
formly documented  and  is  not  always  available.  In  an  attempt  to 
assemble  uniform  weather  modification  activities  information  of  its 
member  nations,  the  World  Meteorological  Organization  (WMO)  in 
1975  instigated  a  system  of  reporting  and  of  maintaining  a  register  on 
such  activities.  Under  this  arrangement  25  nations  reported  weather 
modification  projects  during  1976,  and  16  countries  provided  similar 
information  in  1975.  The  largest  weather  modification  effort  outside 
the  United  States  is  in  the  Soviet  Union,  where  there  are  both  a  con- 
tinuing research  program  and  an  expanding  operational  program.  The 
latter  is  primarily  a  program  designed  to  reduce  crop  damage  from 
hail,  the  largest  such  effort  in  the  world,  covering  about  5  million 
hectares  (15  million  acres)  in  1976.  Other  countries  with  weather  modi- 
fication programs  of  some  note  include  Canada,  Israel,  Mexico,  and 
the  People's  Republic  of  China.  Projects  in  Rhodesia  and  the  Republic 
of  South  Africa  are  not  reported  through  the  WMO  register  since 
these  countries  are  not  WMO  member  nations. 

Recent  years  have  seen  increased  international  awareness  of  the 
potential  benefits  and  possible  risks  of  weather  modification  technology 
and  increased  international  efforts  to  control  such  activities.  The  major 
efforts  of  the  international  community  in  this  area  are  to  encourage 
and  maintain  the  high  level  of  cooperation  which  currently  exists  in 
weather  prediction  and  research  and  to  insure  that  man's  new  abilities 
will  be  used  for  peaceful  purposes.  There  has  been  exchange  of  ideas 
on  weather  modification  through  international  conferences  and 
through  more  informal  exchanges  of  scientists  and  research  documents. 
As  with  many  scientific  disciplines,  however,  the  problems  arising 
from  use  of  and  experiments  with  weather  modification  are  not  just 
scientific  in  nature,  but  are  political  problems  as  well. 

In  addition  to  the  problems  of  potential  damage  to  countries  through 
commercial  or  experimental  weather  modification  activities,  another 
growing  area  of  concern  is  that  weather  modification  will  be  used  for 
hostile  purposes  and  that  the  future  will  bring  weather  warfare  be- 
tween nations.  The  United  States  has  already  been  involved  in  one 


such  instance  during  the  Vietnam  war  when  attempts  were  made  to 
impede  traffic  by  increasing  rainfall  during  the  monsoon  season.  In  the 
future,  even  the  perception  that  weather  modification  techniques  are 
available  or  in  use  could  lead  to  an  increase  in  international  tensions. 
Natural  drought  in  a  region,  or  any  other  natural  disaster  will  be 
suspect  or  blamed  on  an  enemy. 

In  light  of  these  problems  the  international  community  has  made 
scattered  attempts  both  to  further  the  study  of  weather  and  its  modifi- 
cation and  to  insure  the  peaceful  use  of  this  new  technology.  One  such 
attempt  was  the  development  of  the  Convention  on  the  Prohibition 
of  Military  or  Any  Other  Hostile  Use  of  Environmental  Modification 
Techniques,  which  was  adopted  by  the  General  Assembly  of  the  United 
Nations  and  opened  for  signature  on  May  18. 19TT,  at  which  time  it  was 
signed  by  the  United  States  and  33  other  nations  (though  it  has  not 
yet  been  submitted  to  the  U.S.  Senate  for  ratification) .  Another  exam- 
ple of  promotion  of  peaceful  use  of  weather  modification  is  the  Pre- 
cipitation Enhancement  Program,  sponsored  by  the  WMQ,  whose  aim 
is  to  plan,  set  up,  and  carry  out  an  international,  scientifically  con- 
trolled precipitation  experiment  in  a  semiarid  region  of  the  world 
under  conditions  where  the  chances  are  optimal  for  increasing  pre- 
cipitation in  sufficient  amounts  to  produce  economic  benefits. 

The  United  Nations  Conference  on  the  Human  Environment,  held 
in  June  1972  in  Stockholm,  has  been  the  pivotal  point  in  much  recent 
international  environmental  activity.  It  too  has  been  an  important 
catalyst  in  international  activities  relating  to  weather  modification 
through  portions  of  its  "Declaration,"  its  "Action  Plan  for  the  Human 
Environment,"  its  "Earthwatch  Program,"  and  its  "Study  of  Man's 
Impact  on  Climate." 

Legal  issues  in  weather  modification  are  complex  and  unsettled. 
They  can  be  considered  in  at  least  four  broad  categories :  private  rights 
in  the  clouds,  liability  for  weather  modification,  interstate  legal  issues, 
and  international  legal  issues.  Since  the  body  of  law  on  weather  modi- 
fication is  slight,  existing  case  law  offers  few  guidelines  to  determine 
these  issues.  Regarding  the  issue  of  private  rights  in  the  clouds,  there 
is  no  general  statutory  determination  of  ownership  of  atmospheric 
water,  so  it  is  often  necessary  to  use  analogies  to  some  general  common 
law  doctrines  pertaining  to  water  distribution,  although  each  such 
doctrine  has  its  own  disadvantages  when  applied  to  weather  modifica- 
tion. Some  State  laws  reserve  ownership  or  right  to  use  atmospheric 
water  to  the  State. 

Issues  of  liability  for  damage  may  arise  when  drought,  flooding, 
or  other  severe  weal  her  phenomena  occur  following  attempts  to  modify 
the  weather.  Such  issues  include  causation,  nuisance,  strict  liability, 
trespass,  negligence,  and  charges  of  pollution  of  the  air  and  water 
through  introduction  of  artificial  nucleants.  Statutes  of  10  States  dis- 
cuss weather  modification  liability:  however,  there  is  much  variation 
among  the  specific  provisions  of  the  laws  in  those  States.  Before  a 
case  can  be  made  for  liability  based  on  causation,  it  must  be  pro\en 
that  the  adverse  weather  conditions  were  indeed  induced  by  the  wen:  r 
modifier;  but,  in  fact,  no  one  lias  ever  been  able  to  establish  causation 
of  damages  through  such  activities  in  view  of  the  scientific  uncer- 
tainties of  weather  modification. 


Significant  issues  may  arise  when  weather  modification  activities 
conducted  in  one  State  affect  another  State  as  well.  There  may  be,  for 
example,  the  claim  that  seeding  in  one  State  has  removed  from  the 
clouds  water  that  should  have  fallen  in  an  adjacent  State  or  that 
excessive  flooding  resulted  from  cloud  seeding  in  a  State  upwind. 
Operation  of  cloud-seeding  equipment  near  the  border  of  one  State 
may  also  violate  local  or  State  regulations  or  prohibitions  of  such 
operations  in  that  State.  There  have  been  some  attempts  to  resolve  these 
and  other  issues  through  specific  legislation  in  some  States  and  through 
informal  bilateral  agreements.  While  no  formal  compacts  currently 
exist,  some  compacts  allocating  waters  in  interstate  streams  may  be 

Because  atmospheric  processes  operate  independent  of  national 
borders,  weather  modification  is  inherently  of  international  concern, 
and.  international  legal  issues  have  similarities  to  domestic  interstate 
activities  and  dangers.  Whereas  domestic  weather  modification  law  is 
confused  and  unsettled,  international  law  in  this  area  is  barely  in  the 
formative  stage.  In  time,  ramifications  of  weather  modification  may 
lead  to  major  international  controversy. 

Whereas  the  potential  for  long-term  economic  gains  through  weather 
modification  cannot  be  denied,  current  economic  analyses  are  tenuous  in 
view  of  present  uncertainty  of  the  technology  and  the  complex  nature 
of  attendant  legal  and  economic  problems.  Economic  evaluation  of 
weather  modification  activities  has  therefore  been  limited  to  special, 
localized  cases,  such  as  the  dispersal  of  cold  fog  at  airports,  where 
benefit-cost  ratios  greater  than  5  to  1  have  been  realized  through  sav- 
ings in  delayed  or  diverted  traffic.  It  has  also  been  estimated,  on  the 
basis  of  a  15-percent  increase  in  snowpack  through  seeding  orographic 
clouds,  that  about  2  million  additional  acre-feet  of  water  per  year 
could  be  produced  in  the  Colorado  River  Basin,  at  a  cost  of  about 
$1.50  per  acre-foot. 

Costs  of  most  weather  modification  operations  are  generally  small 
in  relation  to  other  costs  in  agriculture,  for  example,  and  are  normally 
l>elieved  to  be  only  a  fraction  of  the  benefits  which  could  be  achieved 
from  successful  operations.  However,  if  all  the  benefits  and  all  the  costs 
are  considered,  benefit-cost  ratios  may  be  diminished.  While  direct  co«ts 
and  benefits  from  weather  modification  are  reasonably  apparent,  in- 
direct costs  and  benefits  are  elusive  and  require  further  study  of 
sociological,  legal,  and  ecological  implications. 

There  are  numerous  cases  of  both  real  and  perceived  economic  losses 
which  one  or  more  sectors  of  the  public  may  suffer  while  another 
group  is  seeking  economic  advantage  through  some  form  of  weather 
modification.  Overall  benefits  from  weather  modification  are  accord- 
ingly reduced  when  net  gains  are  determined  from  such  instances  of 
mixed  economic  advantages  and  disadvantages.  In  fact,  when  mecha- 
nisms are  established  for  compensating  those  who  have  suffered  losses 
resultinof  from  weather  modification,  benefits  to  those  groups  seeking 
economic  gain  through  such  projects  will  probably  be  accordingly 

Economically  significant  weather  modification  activities  will  have 
an  eventual  ecological  effect,  though  appearance  of  that  effect  may  be 
hidden  or  delayed  by  system  resilience  and/or  confused  by  system 


complexity.  Prediction  of  ecological  effects  may  never  be  possible  with 
any  precision;  however,  the  greater  the  precision  with  which  the 
weather  modifier  can  predict  results  of  his  activities,  the  more  pre- 
cisely can  the  ecologist  predict  ecological  effects.  Such  effects  will 
rarely  be  sudden  or  catastrophic,  but  will  result  from  moderate 
weather-related  shifts  in  rates  of  reproduction,  growth,  and  mortality 
of  plants  and  animals.  Adjustments  of  plant  and  animal  communities 
will  thus  occur  more  slowly  in  regions  of  highly  variable  weather  than 
in  those  with  more  uniform  conditions  which  are  slowly  changing  with 
some  regularity  over  time.  Deliberate  weather  modification,  such  as 
precipitation  augmentation,  is  likely  to  have  a  greater  ecological  im- 
pact in  semi-arid  regions  than  in  humid  ones. 

Widespread  cloud  seeding,  using  silver  iodide,  could  result  in  esti- 
mated local,  temporary  increases  in  silver  concentrations  in  precipita- 
tion approaching  those  in  natural  waters,  but  exchange  rates  would  be 
an  order  of  magnitude  lower  than  the  natural  exchange  rates.  Ex- 
change rates  will  likely  be  many  orders  of  magnitude  less  than  those 
rates  at  which  plants  and  soils  are  adversely  affected. 


1.  Weather  modification  is  an  emerging  technology ;  there  is  a  wide 
spectrum  of  capabilities  to  modify  various  weather  phenomena,  rang- 
ing from  the  operational  readiness  of  cold  fog  dispersal  to  little  prog- 
ress beyond  initial  research  in  the  case  of  modifying  severe  storms 
such  as  hurricanes. 

2.  Along  with  cold  fog  dispersal,  the  only  other  weather  modifica- 
tion capability  showing  near  readiness  for  application  is  the  aug- 
mentation of  winter  snowpack  through  seeding  mountain  cloud  sys- 
tems. A  probable  increase  of  about  15  percent  is  indicated  by  a  number 
of  experiments  and  longrunning  operational  seeding  projects  in  the 
western  United  States. 

3.  Most  scientists  and  weather  modification  operators  agree  that 
there  is  continued  need  for  a  wide  range  of  research  and  development 
activity  both  to  refine  weather  modification  techniques  where  there 
has  been  some  success  and  to  advance  capabilities  in  modifying  other 
weather  phenomena  where  there  has  been  much  less  or  little  progress. 

4.  Current  Federal  policy  for  weather  modification  research  and 
development  follows  the  mission-oriented  approach,  where  each  agency 
charged  with  responsibility  for  dealing  with  a  particular  national 
problem  is  given  latitude  to  seek  the  best  approach  or  solution  to  the 
problem;  this  approach  or  solution  may  involve  weather  modification. 

5.  The  structure  of  Federal  organization  for  weather  modification 
reflects  the  mission-oriented  approach  which  is  characteristic  of  the 
current  Federal  policy,  the  programs  loosely  coordinated  through  ad- 
visory groups  and  the  Interdepartmental  Committee  for  Atmospheric 

0.  The  interest  of  the  Congress  in  weather  modification  has  been 
shown  by  the  introduction  of  110  bills  related  to  the  subject  since 
1017 — 0  of  which  have  become  public  law — and  the  consideration  of  22 
resolutions  on  weather  modification,  one  of  which  was  passed  by  the 

7.  A  number  of  major  weather  modification  policy  studies  have  been 
directed  by  public  law  or  initiated  within  the  executive  branch  over 


the  past  25  years ;  most  of  these  studies  recommended  designation  of 
a  lead  agency,  increased  basic  meteorological  research,  increased  fund- 
ing, improvement  of  support  and  cooperation  from  agencies,  and  con- 
sideration of  legal,  socioeconomic,  environmental,  and  international 
aspects.  Although  some  recommended  actions  have  been  undertaken, 
others  have  not  seen  specific  action  to  date. 

8.  While  major  policy  studies  have  recommended  increased  funding 
for  Federal  weather  modification,  research  and  development  and  fund- 
ing has  generally  increased  over  the  past  20  years,  recommended  levels 
have  been  consistently  higher  than  those  provided,  and  funding  has 
actually  decreased  since  fiscal  year  1976. 

9.  With  enactment  of  the  National  Weather  Modification  Policy 
Act  of  1976  and  completion  of  the  major  policy  study  mandated  by 
that  act,  there  is  a  fresh  opportunity  for  the  Congress  to  assess  the 
potential  usefulness  and  problems  in  application  of  weather  modifica- 
tion technology  and  to  establish  a  new  Federal  policy  for  weather 
modification  research  and  operations. 

10.  The  principal  role  in  regulating  weather  modification  and  in 
supporting  operational  programs  has  been  taken  by  the  States,  while 
the  role  of  the  Federal  Government  has  been  support  of  research  and 
development  programs. 

11.  The  majority  of  the  States  (29)  have  some  form  of  law  which 
relates  to  weather  modification,  and  the  general  policy  of  a  State 
toward  weather  modification  is  usually  reflected  in  the  weather  modi- 
fication law  of  that  State ;  laws  of  some  States  tend  to  encourage  devel- 
opment and  use  of  the  technology,  while  others  discourage  such 

12.  The  majority  of  operational  weather  modification  projects  in  the 
United  States  (58  of  a  total  of  72,  or  80  percent  in  calendar  year  1975) 
are  conducted  west  of  Kansas  City,  and  the  largest  number  of  projects 
has  been  in  California  (20  during  1977) ;  most  operational  projects 
are  intended  to  increase  precipitation,  while  others  are  designed  to 
suppress  hail  or  disperse  fog. 

13.  Both  the  greatest  support  and  the  strongest  opposition  to  weather 
modification  projects  are  focused  at  the  local  level,  where  the  economic 
and  personal  interests  of  local  organizations  and  individuals  are  most 
directly  affected;  it  follows  that  there  is  also  the  least  social  stress 
when  decisions  to  apply  or  withhold  weather  modification  are  made 
at  the  local  level. 

14.  Commercial  weather  modification  operators  have  substained  ac- 
tivities since  the  early  days,  after  which  some  operations  fell  into 
disrepute,  providing  a  valuable  data  base  for  evaluation  of  long-term 
projects  and  developing  expertise  over  a  broad  range  of  capabilities: 
most  have  incorporated  improvements  into  their  technology  as  they 
have  benefited  from  accumulated  experience  and  from  research  results. 

15.  While  the  United  States  is  the  apparent  leader  in  overall  research 
and  operational  weather  modification  activities,  there  have  been  ap- 
proximately 20  foreign  countries  in  which  activities  are  conducted  an- 
nually (25  countries  reported  such  projects  for  1976  through  the 
register  of  the  World  Meteorological  Organization)  ;  the  largest  for- 
eign program  is  that  of  the  Soviet  Union,  whose  operational  hail 
suppression  program  covered  about  15  million  acres  in  1976,  the  largest 
such  effort  in  the  world. 


16.  The  international  community  has  attempted  to  further  the  study 
o  f  weather  modification  and  insure  its  peaceful  use  through  the  recent 
development  of  a  Convention  on  the  Prohibition  of  Military  or  Any 
Other  Hostile  Use  of  Environmental  Techniques  (adopted  by  the 
U.N.  General  Assembly  and  opened  for  signature  in  May  1977)  and 
through  sponsorship  by  the  World  Meteorological  Organization  of 
an  international  precipitation  enhancement  program. 

17.  Legal  issues  in  weather  modification  are  complex  and  unsettled; 
they  include  resolution  of  problems  of  ownership  of  atmospheric  water, 
issues  of  liability,  conflicting  statutes  and  regulations  of  respective 

e  laws,  and  the  need  to  develop  a  regime  of  relevant  international 


18.  Although  the  long-term  potential  for  economic  gains  through 
weather  modification  cannot  be  denied,  attempts  to  quantify  benefits 
mnd  costs  from  such  activities  will  in  most  cases  be  difficult  to  undertake 
on  a  practical  basis  until  the  technology  is  more  highly  developed  and 
control  systems  are  perfected  to  permit  reliable  predictions  of 

19.  Economically  significant  wreather  modification  will  always  have 
an  eventual  ecological  effect,  though  appearance  of  the  effect  may  be 
delayed  or  hidden  by  system  resilience  and/or  confounded  by  system 
complexity ;  the  more  precisely  the  weather  modifier  can  specify  effects 
lie  will  produce,  the  more  precise  can  be  the  ecologist's  prediction  of 
likely  ecological  effects. 

20.  Modification  processes  may  also  be  initiated  or  triggered  inad- 
vertently rather  than  purposefully ;  man  is  already  causing  measurable 
variations  unintentionally  on  the  local  scale,  and  artificial  climate 
effects  have  been  observed  on  local  and  regional  scales.  Although  not 
veri  fiable  at  present,  the  time  may  not  be  remote  when  human  activities 
will  result  in  measurable  large-scale  changes  in  weather  and  climate 
of  more  than  passing  significance. 



(I?y  Robert  E.  Morrison,  Specialist  in  Earth  Sciences,  Science  Policy  Research 
Division,  Congressional  Research  Service) 


uIt  is  entirely  possible,  were  he  wise  enough,  that  man  could  produce 
favorable  effects,  perhaps  of  enonnous  practical  significance,  trans- 
forming his  environment  to  render  it  more  salutary  for  his  purposes. 
This  is  certainly  a  matter  which  should  be  studied  assiduously  and 
explored  vigorously.  The  first  steps  are  clear.  In  order  to  control 
meteorological  matters  at  all  we  nee  d  to  understand  them  better  than 
we  now  do.  When  we  understand  fully  ice  can  at  least  predict  weather 
with  assurance  for  reasonable  intervals  in  the  future. 

''With  modem  analytical  devices,  with  a  team  of  sound  background 
and  high  skills,  it  is  possible  today  to  do  a  piece  of  work  in  this  field 
which  will  render  immediate  benefits,  and  carry  us  for  toward  a  more 
thorough  understanding  of  ultimate  possibilities.  By  all  means  let  us 
get  at  it." 

— Vanne var  Bush  1 


Two  decades  after  completion  of  a  major  study  and  report  on 
weather  modification  by  the  Advisory  Committee  on  Weather  Control 
and  after  the  assertions  quoted  above,  many  would  agree  that  some 
of  the  more  fundamental  questions  about  understanding  and  using 
weather  modification  remain  unsolved.  There  is  a  great  difference  of 
opinion,  however,  on  the  state  of  technology  in  this  field.  According 
to  Grant,  "Some  believe  that  weather  modification  is  now  ready  for 
widespread  application.  In  strong  contrast,  others  hold  that  applica- 
tion of  the  technology  may  never  be  possible  or  practical  on  any 
substantial  scale."  2  It  has  been  demonstrated  that  at  least  some  atmos- 
pheric phenomena  can  be  modified  with  some  degree  of  predictable 
success,  as  a  consequence  of  seeding  supercooled  clouds  with  artificial 
ice  nuclei,  and  there  is  some  promise  that  the  present  technology  will 
be  expanded  to  include  a  greater  scope  of  weather  modification  capa- 
bilities. Nevertheless,  a  systematic  approach  and  reasonable  progress 
in  development  of  weather  modification  technology  have  been  impeded 
by  a  number  of  problems. 

Changnon  asserts  that  a  continuing  and  overriding  problem  restrict- 
ing progress  has  been  the  attempt  to  apply  an  ill-defined  technology 
to  increase  rain  or  suppress  hail  without  an  adequate  scientific  under- 

1  From  statement  of  Dec.  2,  1957,  quoted  in  final  report  of  the  Advisory  Committee  on 
Weather  Control,  Washington,  D.C.,  U.S.  Government  Printing  Office.  1958.  vol.  I.  p.  1. 

2  Grant,  Lewis  O.,  "Scientific  and  Other  Uncertainties  of  Weather  Modification.  In 
William  A.  Thomas  (editor),  Legal  and  Scientific  Uncertainties  of  Weather  Modification. 
Proceedings  of  a  symposium  convened  at  Duke  University.  Mar.  11-3  2.  1976,  by  the 
National  Conference  of  Lawyers  and  Scientists,  Durham,  N.C.,  Duke  University  Press, 
1977,  p.  7. 


34-857—79  3 


standing  and  predictable  outcome.3  Experimentation  has  been  poorly 
conducted,  intermittent,  or  too  short ;  and  "results  have  not  been  inte- 
grated with  those  of  other  projects  so  as  to  develop  a  continuing  thread 
of  improving  knowledge."  4 

In  response  to  the  query  as  to  why  progress  in  weather  modification 
lias  been  so  slow,  Fleagle  identifies  three  broad,  general  impediments. 
"First,  the  physical  processes  associated  with  clouds  have  turned  out  to 
be  especially  complex  and  difficult  *  *  *.  A  second  possibility  may  be 
that  the  atmosphere  is  inherently  stable,  so  that  within  broad  limits,  no 
matter  what  we  do  to  increase  precipitation,  the  results  are  likely  to  be 
small  and  roughly  the  same  *  *  *.  A  third  reason  *  *  *  is  that  progress 
has  been  hamstrung  by  fragmentation  of  resources,  by  submarginal 
funding,  ineffective  planning  and  coordination,  and  a  general  lack  of 
administrative  toughness  and  fiscal  stability."  5 

Droessler  points  out  the  need  to  "formulate  a  comprehensive  national 
weather  modification  policy  which  has  the  broad  support  of  the  scien- 
tific community,  the  general  public,  private  industry,  and  the  Govern- 
ment," contending  that  "the  greatest  deterrent  in  getting  on  with  the 
task  of  preparing  a  satisfactory  national  policy  is  the  lack  of  a  con- 
sensus about  the  national  goals  for  weather  modification."  6 

Although  operational  readiness  varies  from  one  form  of  weather 
modification  to  another,  as  a  result  of  the  degree  of  understanding  and 
the  complexity  of  decisionmaking  in  given  situations,  the  prospects  for 
successful  weather  modification  are  sufficiently  promising  that  at- 
tempts to  develop  effective  applications  will  continue.  This  was  one  of 
the  major  areas  of  co?isensus  at  a  recent  symposium  on  the  uncertainties 
of  weather  modification : 

There  will  be  increased  attempts  to  modify  weather,  both  because  people  tend 
to  do  what  is  technically  possible  and  because  the  anticipated  benefits  of  precipi- 
tation augmentation,  hail  or  lightning  suppression,  hurricane  diversion,  and  other 
activities  often  exceed  the  associated  costs.7 

With  the  inevitable  increases  in  weather  modification  capabilities 
and  the  increasing  application  of  these  capabilities,  the  development  of 
a  technology  that  is  socially  useful  must  be  insured  through  a  careful 
analysis  of  attendant  benefits  and  disbenefits.  According  to  Fleagle. 
et  al..  deliberate  efforts  to  modify  the  weather  have  thus  far  had  only 
marginal  societal  impacts;  however,  as  future  activities  expand,  "they 
will  probably  be  accompanied  by  secondary  effects  which  in  many 
instances  cannot  be  anticipated  in  detail  *  *  *."  Consequently,  "rational 
policy  decisions  are  urgently  needed  to  insure  that  activities  are  di- 
rected toward  socially  useful  goals."  8 

The  lack  of  a  capability  to  deal  with  impending  societal  problems 

8  Changnori,  Stanley  A..  Jr..  "The  Federal  Role  In  Weather  Modification."  bgckgrbund 
paper  prepared  for  use  by  the  U.S.  Department  of  Commerce  Weather  Modification  Advi- 
sory Board.  Mar.  !).  3  077,  p.  5. 

'  Ibid.,  pp.  ">-G. 

s  Fleagle.  Robert  O..  "An  Analysis  of  Federal  Policies  in  Weather  Modification.''  back- 
ground paper  prepared  for  use  by  the  U.S.  Department  of  Commerce  Weather  Modification 
Adv:s<  rv  Hoard.  Mar.  1<»77.  pp.  17-18. 

«  Droessler,  Farl  (»..  "Weather  Modification"  (Federal  Policies.  Funding  From  AIT 
Sources  Interagency  Coordination),  background  paper  prepared  for  use  of  the  U.S.  Depart- 
ment of  Commerce  Weather  Modification  Advisory  Board,  Mar.  l.  l!>77.  p.  10 

7  Thomas.  William  A.  (editor).  "Legal  and  Scientific  Uncertainties  of  Weather  Modifie-i- 
tion,"  proceedings  of  a  Symposium  convened  at  Duke  University.  Mar  11-12.  1970,  by  the 
Vf»'onal  Conference  of  Lawyers  and  Scientists.  Durham,  N.C.,  Dnke  Universitv  Pres., 
1077,  p.  vl. 

Flt*agie.  Robert  r>  •  -lames  A.  Crutchfteld,  Ralph  W.  Johnson,  and  Mohamed  F.  AbdO, 
"Weather  Modification  in  the  PUbllC  Interest."  Seattle,  American  Meteorological  Society 

and  the  University  of  Washington  Press,  i<>73.  p.  3,  31-32. 


and  emerging  management  issues  in  weather  modification  has  been 
aphoristically  summed  up  in  the  following  statement  by  Crutchfield: 

Weather  modification  is  in  the  throes  of  a  serious  schizoid  process  The  slow 
and  sober  business  of  piecing  together  the  scientific  knowledge  of  weather  proc- 
esses developing  the  capacity  to  model  the  complex  systems  involved,  and  assess- 
ing systematically  the  results  of  modification  efforts  has  led  to  responsible  opti- 
mism about  the  future  of  these  new  technologies.  On  the  other  hand,  the  social 
technology"  of  evaluation,  choice,  and  execution  has  lagged  badly.  Ihe  present  de- 
cisionmaking apparatus  appears  woefully  inadequate  to  the  extraordinarily  ^diffi- 
cult task  of  fitting  weather  modification  into  man  s  pattern  of  life  m  optimal 
fashion  There  are' too  many  game  plans,  too  many  coaches,  and  a  disconcerting 
proclivity  for  running  hard  before  deciding  which  goal  line  to  aim  for— or,  indeed, 
which  field  to  play  on.  ,J  .  .  .  _  . 

Mounting  evidence  indicates  that  weather  modification  of  several  types  is, 
or  may  soon  become  technically  feasible.  That  some  groups  will  derive  economic 
or  other  social  benefits  from  such  technology  is  a  spur  to  action.  But  a  whole 
thunderhead  of  critical  questions  looms  on  the  horizon  waiting  to  be  resolved 
before  any  valid  decisions  can  be  made  about  the  scale,  composition,  location, 
and  management  of  possible  operations.9 


In  a  study  for  the  Interdepartmental  Committee  for  Atmospheric 
Sciences,  Homer  E.  Newell  highlighted  the  potential  benefits  of  inten- 
tional weather  modification  : 

The  Earth's  weather  has  a  profound  influence  on  agriculture,  forestry,  water 
resources,  industry,  commerce,  transportation,  construction,  field  operations, 
commercial  fishing,  and  many  other  human  activities.  Adverse  effects  of  weather 
on  man's  activities  and  the  Earth's  resources  are  extremely  costly,  amounting 
to  billions  of  dollars  per  year,  sometimes  causing  irreparable  damage  as  when 
human  lives  are  lost  in  severe  storms.  There  is,  therefore,  great  motivation 
to  develop  effective  countermeasures  against  the  destructive  effects  of  weather, 
and,  conversely,  to  enhance  the  beneficial  aspects.  The  financial  and  other  ben- 
efits to  human  welfare  of  being  able  to  modify  weather  to  augment  water 
supplies,  reduce  lightning,  suppress  hail,  mitigate  tornadoes,  and  inhibit  the  full 
development  of  hurricanes  would  be  very  great.10 

More  recently.  Louis  J.  Battan  gave  the  following  two  reasons,  with 
graphic  examples,  for  wanting  to  change  the  weather : 

First,  violent  weather  kills  a  great  many  people  and  does  enormous  property 
damage.  A  single  hurricane  that  struck  East  Pakistan  in  Novemlier  1970  killed 
more  than  250,000  people  in  a  single  day.  Hurricane  Camille  hit  the  United  States 
in  1969  and  did  approximately  $1.5  billion  worth  of  damage.  An  outbreak  of 
tornadoes  in  the  Chicago  area  on  Palm  Sunday  of  1965  killed  about  250  people, 
and  the  tornadoes  of  April  1974  did  likewise.  Storms  kill  people  and  damage 
property,  and  it  is  reasonable  to  ask  whether  it  is  necessary  for  us  to  accept 
this  type  of  geophysical  destruction.  I  say,  "No,  it  is  not — it  should  be  possible 
to  do  something." 

Second,  weather  modification  involves,  and  in  some  respects  might  control, 
the  production  of  those  elements  we  need  to  survive.  Water  and  food  are  cur- 
rently in  short  supply  in  many  areas,  and  these  shortages  almost  certainly  will 
be  more  severe  in  the  future.  We  can  develop  new  strains  of  wheat  and  rye  and 
corn  and  soybeans  and  rice,  but  all  is  for  naught  if  the  weather  fails  to  coop- 
erate. If  the  monsoons  do  not  deliver  on  schedule  in  India,  residents  of  that 
country  starve  in  large  numbers.  And  if  the  drought  that  people  have  been 
predicting  for  the  last  several  years  does  spread  over  the  Great  Plains,  there 
will  be  starvation  around  the  world  on  a  scale  never  before  experienced. 

Weather  is  the  one  uncontrollable  factor  in  the  whole  business  of  agriculture. 
Hail,  strong  winds,  and  floods  are  the  scourges  of  agriculture,  and  we  should 
not  have  to  continue  to  remain  helpless  in  the  face  of  them.  It  may  be  impossible 

9  Crntehfielri.  James  A..  "Social  CVoice  and  Weather  Modification  :  Concepts  and  Measure- 
ment of  Impact."  In  W.  R.  Derrick  Sewell  (editor).  Modifying  the  Weather:  a  Social 
Assessment,  Victoria,  British  Columbia.  University  of  Victoria.  1978.  p.  1S7. 

10  Newell.  Homer  E.,  "A  Recommended  National  Program  in  Weather  Modification."  Fed- 
eral Council  for  Science  and  Technology,  Interdepartmental  Committee  for  Atmospheric 
Sciences,  ICAS  report  No.  10a,  Washington,  D.C.,  November  1966,  p.  1. 


for  us  to  develop  the  kind  of  technology  we  would  like  to  have  for  modification 
of  weather,  but  to  assume  failure  in  such  an  important  endeavor  is  a  course 
not  to  be  followed  by  wise  men.11 

Specific  statistics  on  annual  losses  of  life  and  economic  losses  from 
property  damages  resulting  from  weather-related  disasters  in  the 
United  States  are  shown  in  table  1,  which  wras  developed  in  a  recent 
study  by  the  Domestic  Council.12  In  the  table,  for  comparison,  are 
the  fiscal  year  1975  expenditures  by  the  Federal  Government  in 
weather  modification  research,  according  to  the  several  categories  of 
weather  phenomena  to  be  modified.  Although  it  is  clear  that  weather 
disasters  can  be  mitigated  only  partially  through  weather  modifica- 
tion, even  if  the  technology  were  fully  developed,  the  potential  value, 
economic  and  otherwise,  should  be  obvious.  The  following  quotation 
from  a  Federal  report  written  over  a  decade  ago  summarizes  the  full 
potential  of  benefits  to  mankind  which  might  be  realized  through  use 
of  this  technology : 

With  advances  in  his  civilization,  man  has  learned  how  to  increase  the  fruit 
of  the  natural  environment  to  insure  a  livelihood.  *  *  *  it  is  fortunate  that 
growing  knowledge  of  the  natural  world  has  given  him  an  increasing  awareness 
of  the  changes  that  are  occurring  in  his  environment  and  a' so  hopefully  some 
means  for  deliberate  modification  of  these  trends.  An  appraisal  of  the  prospects 
for  deliberate  weather  and  climate  modification  can  be  directed  toward  the 
ultimate  goal  of  bringing  use  of  the  environment  into  closer  harmony  with  its 
capacities  and  with  the  purposes  of  man — whether  this  be  for  food  production, 
relief  from  floods,  assuring  the  continuance  of  biologic  species,  stopping  pollu- 
tion, or  for  purely  esthetic  reasons.13 


Property  Modification 
damage1  research 

Weather  hazard  Loss  of  life1        (billions)  (millions) 

Hurricanes                                                                                      2  30  2  $rj.  8  3  $o.  8 

Tornadoes  .                                                             2140  2.4  4  1.0 

Hail   5.8  3.9 

Lightning                                                                                    « 110  .1  .4 

Fog                                                                                           M.000  7.5  1.3 

Floods                                                                                          6  240  8  2.3 

Frost  (agriculture)   7  1. 1   

Drought    7.7  93.4 

Total   1,520  6.7  10.8 

1  Sources:  "Assessment  of  Research  on  Natural  Hazards,"  Gilbert  F.  White  and  J.  Eugene  Haas,  the  MIT  Press,  Cam- 
bridge, Mass.,  1975,  pp  68,  286,  305,  374;  "The  Federal  Plan  for  Meteorological  Services  and  Supporting  Research,  Fiscal 
Year  1976,"  U.S.  Department  of  Commerce,  National  Oceanic  and  Atmospheiic  Administration  (NOAA),  Washington,  D.C., 
April  1975,  p  9;  "Weatheiwise,"  February  1971,  1972,  1973,  1974,  1975,  American  Meteorological  Society,  Boston,  Mass.; 
"Summary  Report  on  Weather  Modification,  Fiscal  Years  1969,  1970,  1971,"  U.S.  Department  of  Commerce,  NOAA,  Wash- 
ington, D.C.,  May  1973,  pp  72,  81;  "Estimating  Crop  Losses  Due  to  Hail — Wot  king  Data  for  County  Estimates,"  U.S.  De- 
partment of  Agriculture,  Economic  Research  Service,  September  1974;  "Natural  Disasters:  Some  Empirical  and  Economic 
Considerations,"  G.  Thomas  Sav,  National  Bureau  of  Standards,  Washington,  D.C.,  February  1974,  p  19;  Traffic  Safety 
magazine,  National  Safety  Council,  February  1974. 

2  1970-74  average. 

3  These  funds  do  not  include  capital  investment  in  research  aircraft  and  instrumentation  primarily  for  hurricane  modi- 
fication, which  in  fiscal  year  1975  amounted  to  $9,200,000. 

4  These  funds  support  theoretical  research  on  modification  of  extratropical  cloud  systems  and  their  attendant  severe 
storms  such  as  thunderstorms  and  tornadoes. 

5  1973. 

«  1950-72  average. 

7  Average. 

1  1965-69  average. 

9  These  funds  support  precipitation  augmentation  research,  much  of  which  may  not  have  direct  application  to  drought 

11  Battan,  Louis  J..  "The  Scientific  Uncertainties:  a  Scientisl  Responds."  in  William  A. 
Thomas  (editor),  "Legal  and  Scientific  Uncertainties  of  Weather  Modification."  proceed- 
ings of  a  symposium  Convened  at  Duke  University,  .Mar.  11-12,  197©,  by  C  e  National  Con- 
ference of  Lawyers  and  Scientists.  Durham.  N.C.,  Duke  University  Press.  1!)77.  p.  20. 

12  U.S  Domestic  Council.  Environmental  Resources  Committee,  Subcommittee  on  Climate 
Change.  "The  Federal  Rofe  in  Weather  Modification,"  December  i(->~r»,  p.  2. 

u»  Special  Commission  on  Weather  Modification.  "Weather  and  Climate  Modification," 
National  Science  Foundation.  NSF  6G-3,  Washington,  D.C.,  Dec.  20,  1965,  p.  7. 



The  modern  period  in  weather  modification  is  about  three  decades 
old,  dating  from  events  in  1946,  when  Schaefer  and  Langmuir  demon- 
strated that  a  cloud  of  supercooled  water  droplets  could  be  transformed 
into  ice  crystals  when  seeded  with  dry  ice.  Activities  and  interests 
among  scientists,  the  commercial  cloud  seeders,  and  Government  spon- 
sors and  policymakers  have  exhibited  a  nearly  10-year  cyclic  behavior 
over  the  ensuing  years.  Each  of  the  three  decades  since  the  late  1940's 
has  seen  an  initial  burst  of  enthusiasm  and  activity  in  weather  modi- 
fication experiments  and/or  operations;  a  midcourse  period  of  con- 
troversy, reservations,  and  retrenchment;  and  a  final  period  of 
capability  assessment  and  policy  examination,  with  the  issuance  of 
major  Federal  reports  with  comprehensive  recommendations  on  a 
future  course. 

The  first  such  period  ended  with  the  publication  of  the  final  report 
of  the  Advisory  Committee  on  Weather  Control  in  1957.14  In  1959, 
Dr.  Robert  Brode,  then  Associate  Director  of  the  National  Science 
Foundation,  summarized  the  significance  of  that  study  in  a  1959 
congressional  hearing : 

For  4  years  the  Advisory  Committee  studied  and  evaluated  public  and  private 
cloud-seeding  experiments  and  encouraged  programs  aimed  at  developing  both 
physical  and  statistical  evaluation  methods.  The  final  report  of  the  com- 
mittee *  *  *  for  the  first  time  placed  before  the  American  public  a  body  of 
available  facts  and  a  variety  of  views  on  the  status  of  the  science  of  cloud 
physics  and  the  techniques  and  practices  of  cloud  seeding  and  weather  modifica- 

The  year  1966  was  replete  with  Government  weather  modification 
studies,  major  ones  conducted  by  the  National  Academy  of  Sciences, 
the  Special  Commission  on  Weather  Modification  of  the  National 
Science  Foundation,  the  Interdepartmental  Committee  for  Atmos- 
pheric Sciences,  and  the  Legislative  Reference  Service  of  the  Library 
of  Congress.  During  that  year,  or  thereabouts,  planning  reports  were 
also  produced  by  most  of  the  Federal  agencies  with  major  weather 
modification  programs.  The  significance  of  that  year  of  reevaluatiori 
and  the  timeliness  for  congressional  policy  action  were  expressed  by 
Hartman  in  his  report  to  the  Congress : 

It  is  especially  important  that  a  comprehensive  review  of  weather  modification 
be  undertaken  by  the  Congress  at  this  time,  for  a  combination  of  circumstances 
prevails  that  may  not  be  duplicated  for  many  years.  For  the  first  time  since 
1957  there  now  exists,  in  two  reports  prepared  concurrently  by  the  National 
Academy  of  Sciences  and  a  Special  Commission  on  Weather  Modification,  created 
by  the  National  Science  Foundation,  a  definitive  appraisal  of  the  entire  scope 
of  this  subject,  the  broad  sweep  of  unsolved  problems  that  are  included,  and 
critical  areas  of  public  policy  that  require  attention.  There  are  currently  before 
the  Congress  several  bills  which  address,  for  the  first  time  since  enactment  of 
Public  Law  85-510.  the  question  of  the  formal  assignment  of  Federal  authority 
to  undertake  weather  modification  programs.  And  there  is  increasing  demand 
throughout  the  country  for  the  benefits  that  weather  modification  may  bring.16 

14  F^tablishment  of  the  Advisory  Committee  on  Weather  Control  by  the  Congress  and  its 
actJ^ties  are  discussed  in  following  chapters  on  the  history  of  weather  modification  and 
on  Federal  activities,  chs.  2  and  5,  respectively.  Recommendations  of  the  final  report  are 
summarized  in  ch.  6.  Other  renorts  mentioned  in  the  following  paragraphs  in  this  section 
are  also  discussed  and  referenced  in  chs.  5  and  6.  ■  \ -  .. 

15  U.S.  Congress.  House  of  Representatives.  Committee  on  Science  and  Astronautics. 
"Weather  Modification."  Hearing.  Sfith  Cong..  1st  sess.,  Feb.  16,  1959.  Washington,  JJ.L., 
U.S.  Government  Printing  OfhYp  19^9.  p  3.  .t  _  _ 

16  Hartman,  Lawton  M.  "Weather  Modification  and  Control.'  Library  of  Comrress, 
Legislative  Reference  Service.  Apr.  27.  1966.  Issued  as  a  committee  print  by  the  Senate 
Committee  on  Commerce.  89th  Cone..  2d  sess.,  Senate  Rept.  No.  1139,  Washington, 

U.S.  Government  Printing  Office,  1966,  p.  1. 


Toward  the  close  of  the  third  decade,  a  number  of  policy  studies  and 
reports  appeared,  starting  in  1973  with  a  second  major  study  by  the 
National  Academy  of  Sciences,  and  including  others  by  the  U.S.  Gen- 
eral Accounting  Office  and  by  the  U.S.  Domestic  Council.  The  major 
study  of  this  period  was  commissioned  by  the  Congress  when  it  enacted 
Public  Law  94-490,  the  National  Weather  Modification  Policy  Act  of 
1976,  in  October  of  1976.  By  that  law  the  Secretary  of  Commerce  was 
directed  to  conduct  a  study  and  to  recommend  the  Federal  policy  and  a 
Federal  research  program  in  weather  modification.  That  study  was 
conducted  on  behalf  of  the  Secretary  of  Commerce  by  a  Weather  Modi- 
fication Advisory  Board,  appointed  by  the  Secretary,  and  the  required 
report  will  be  transmitted  to  the  Congress  during  1978.  The  importance 
of  that  act  and  its  mandated  study  was  assessed  by  Dr.  Robert  M. 
White,  former  Administrator  of  the  National  Oceanic  and  Atmos- 
pheric Administration  (NOAA),  the  Commerce  Department  agency 
with  administrative  responsibilities  and  research  programs  in  weather 
modification : 

The  National  Weather  Modification  Policy  Act  of  197C>  *  *  *  will  influence 
X(  )AA  to  some  degree  during  the  next  year,  and  its  effect  may  have  a  large  impact 
on  the  agency  and  the  Nation  in  future  years.  The  comprehensive  study  of  and 
report  on  weather  modification  that  will  result  from  our  implementation  of  this 
act  will  provide  guidance  and  recommendations  to  the  President  and  the  Congress 
in  the  areas  of  policy,  research,  and  utilization  of  this  technology.  We  look  to  this 
study  and  report  as  an  opportunity  to  help  set  the  future  course  of  a  controversial 
science  and  technology  with  enormous  potential  for  henefit  to  the  Nation.17 

Thus,  conditions  once  more  are  ripe  and  the  stage  has  been  set,  as  in 
1957  and  again  in  1966,  for  the  Congress  to  act  in  establishing  a  defini- 
tive Federal  weather  modification  policy,  one  appropriate  at  least  for 
the  next  decade  and  perhaps  even  longer.  Among  other  considerations, 
such  a  policy  would  define  the  total  role  of  the  Federal  Government, 
including  its  management  structure,  its  responsibilities  for  research 
and  development  and  for  support  operations,  its  authorities  for  regu- 
lation and  licensing,  its  obligation  to  develop  international  cooperation 
in  research  and  peaceful  applications,  and  its  function  in  the  general 
promotion  of  purposeful  weather  modification  as  an  economically  vi- 
able and  socially  accepted  technology.  On  the  other  hand,  other  factors, 
such  as  constraints  arising  from  public  concern  over  spending,  may 
inhibit  the  development  of  such  policy. 

While  some  would  argue  that  there  exists  no  Federal  policy,  at  least 
one  White  House  official,  in  response  to  a  letter  to  the  President,  made 
a  statement  of  weather  modification  policy  in  1975: 

A  considerable  amount  of  careful  thought  and  study  has  been  devoted  to  the 
subject  of  weather  modification  and  what  the  Federal  role  and.  in  particular,  the 
role  of  various  agencies  should  he  in  (his  area.  As  a  result  of  this  study,  we  have 
developed  a  general  strategy  for  addressing  weather  modification  efforts  which 
we  believe  provides  for  an  appropriate  level  of  coordination. 

We  believe  that  the  agency  which  is  charged  with  the  responsibility  for  dealing 
with  a  particular  national  problem  should  Ite  given  the  latitude  to  seek  the  best 
approach  or  solution  to  the  problem.  In  some  instances  this  may  involve  a  form 
of  weather  modification,  while  in  other  instances  other  approaches  may  be  more 

While  we  would  certainly  agree  that  some  level  of  coordination  of  weather 
modification  research  efforts  is  logical,  we  do  not  believe  that  a  program  under 

w  CJ.S.  Congress,  Souse  of  Representatives,  Committee  on  Science  and  Technology.  Sub* 

committi  d  the  EBaTlronmeal  snd  the  Atmosphere.  "Briefing  «"i  the  National  Oceanic  and 

Atmospheric  Administration."  Hearings.  9.1th  Cong.,  1st  sess.,  May  17.  18,  1977.  Washing- 
Jon.  I'.S.  Government  Printing  Ollice,  1977.  i».  4-i5. 


the  direction  of  any  one  single  agency's  leadership  is  either  necessary  or  desirable. 
We  have  found  from  our  study  that  the  types  of  scientific  research  conducted  by 
agencies  are  substantially  different  in  approach,  techniques,  and  type  of  equip- 
ment employed,  depending  on  the  particular  weather  phenomena  being  addressed. 
Each  type  of  weather  modification  requires  a  different  form  of  program  manage- 
ment and  there  are  few  common  threads  which  run  along  all  programs.13 

Presumably,  there  will  be  a  resurgence  of  congressional  interest  in 
weather  modification  policy  during  the  first  session  of  the  96th  Con- 
gress, when  the  aforementioned  report  from  the  Secretary  of 
Commerce  has  been  reviewed  and  considered.  In  view  of  the  recom- 
mendations in  numerous  recent  studies  and  the  opinions  of  the  Weather 
Modification  Advisory  Board  (the  group  of  experts  preparing  the  re- 
port for  the  Secretary  of  Commerce) ,  it  seems  unlikely  that  any  action 
by  the  Congress  would  perpetuate  the  policy  expounded  in  the  White 
House  letter  quoted  above. 

It  is  expected  that  this  present  report,  intended  as  an  overall  review 
of  the  subject  of  weather  modification,  will  be  valuable  and  timely  dur- 
ing the  anticipated  congressional  deliberations. 


In  the  broadest  sense,  weather  modification  refers  to  changes  in 
weather  phenomena  brought  on  purposefully  or  accidentally  through 
human  activity.  Weather  effects  stimulated  unintentionally — such  as 
urban  influences  on  rainfall  or  fogs  produced  by  industrial  com- 
plexes— constitute  what  is  usually  termed  inadvertent  weather  modifi- 
cation. On  the  other  hand,  alterations  to  the  weather  which  are 
induced  consciously  or  intentionally  are  called  planned  or  advertent 
weather  modification.  Such  activities  are  intended  to  influence  single 
weather  events  and  to  occur  over  relatively  short  time  spans,  ranging 
from  a  few  hours  in  the  case  of  clearing  airport  fog  or  seeding  a 
thunderstorm  to  perhaps  a  few  days  when  attempts  are  made  to  re- 
duce the  severity  of  hurricane  winds.  Weather  modification  experi- 
ments or  operations  can  be  initiated  or  stopped  rather  promptly,  and 
changes  resulting  from  such  activities  are  transient  and  generally 
reversible  within  a  matter  of  hours. 

Climate  modification,  by  contrast,  encompasses  changes  of  long-time 
climatic  variables,  usually  affecting  larger  areas  and  with  some  degree 
of  permanence,  at  least  in  the  short  term.  Climatic  changes  are  also 
brought  about  by  human  intervention,  and  they  might  result  from 
either  unintentional  or  planned  activities.  There  are  numerous  ex- 
amples of  possible  inadvertent  climate  modification;  however,  at- 
tempts to  alter  climate  purposefully  are  only  speculative.  The  con- 
cepts of  inadvertent  weather  and  climate  modification  are  defined 
more  extensively  and  discussed  fully  in  chapter  4  of  this  report. 

The  primary  emphasis  of  this  report  is  on  intentional  or  planned 
modification  of  weather  events  in  the  short  term  for  the  general  bene- 
fit of  people,  usually  in  a  restricted  locality  and  for  a  specific  time. 
Such  benefit  may  accrue  through  increased  agricultural  productiv- 

18  Ross,  Norman  E.,  Jr.,  letter  of  June  5,  1975.  to  Congressman  Gilbert  Gude.  This  letter 
was  the  official  White  House  response  to  a  letter  of  April  25.  1975.  from  Congressmen 
Giule  and  Donald  M.  Fraser  and  Senator  Claiborne  Pell,  addressed  to  the  President,  urging 
that  a  coordinated  Federal  program  be  initiated  in  the  peaceful  uses  of  weather  modifica- 
tion. The  letter  to  the  President,  the  replv  from  Mr.  Ross,  and  comments  by  Congressman 
Gude  appeared  in  the  Congressional  Record  for  June  17.  1975,  pp.  19201-19203.  (This 
statement  from  the  Congressional  Record  appears  in  app.  A.) 


ity  or  other  advantages  accompanying  augmentation  of  precipitation 
or  they  may  result  from  mitigation  of  effects  of  severe  weather  with 
attendant  decreases  in  losses  of  life  or  property.  There  are  broader 
implications  as  well,  such  as  the  general  improvement  of  weather  for 
the  betterment  of  man's  physical  environment  for  aesthetic  and  cul- 
tural reasons  as  well  as  economic  ones.  The  following  recent  definition 
sums  up  succinctly  all  of  these  purposes : 

Weather  modification  is  the  deliherate  and  mindful  effort  by  men  and  women 
to  enhance  the  atmospheric  environment,  to  aim  the  weather  at  human  purposes.1" 

The  specific  kinds  of  planned  weather  modification  usually  consid- 
ered, and  those  which  are  discussed,  in  turn,  in  some  detail  in  chapter 
3,  are  the  following: 

Precipitation  enhancement. 

Hail  suppression. 

Fog  dissipation. 

Lightning  suppression. 

Mitigation  of  effects  of  severe  storms. 
Planned  weather  modification  is  usually  considered  in  the  context 
of  its  net  benefits  to  society  at  large.  Nevertheless,  it  should  be  recog- 
nized that,  in  particular  instances,  benefits  to  some  segment  of  the 
population  may  be  accompanied  by  unintended  injuries  and  costs, 
which  may  be  real  or  perceived,  to  other  segments.  There  is  yet  an- 
other aspect  of  advertent  weather  modification,  which  has  engendered 
much  controversy,  both  in  the  United  States  and  internationally,  not 
designed  for  the  benefit  of  those  directly  affected — the  use  of  weather 
modification  for  hostile  purposes  such  as  a  weapon  of  war.  This  aspect 
is  not  a  major  consideration  in  this  report,  although  there  is  some 
discussion  in  chapters  5  and  10  of  congressional  concern  about  such  use 
of  the  technology,  and  in  chapter  10  there  is  also  a  review  of  recent 
efforts  by  the  United  Nations  to  develop  a  treaty  barring  hostile  use 
of  weather  modification.20 

Following  this  introductory  chapter,  witli  its  summary  of  issues, 
the  second  chapter  sets  the  historical  perspective  for  weather  modi- 
fication, concentrating  primarily  on  activities  in  the  United  States  to 
about  the  year  1970,  The  third  chapter  attempts  to  review  the  scien- 
tific background,  the  status  of  technology,  and  selected  technical  prob- 
lems areas  in  planned  weather  modification;  while  chapter  4  contains 
a  discussion  of  weather  and  climate  changes  induced  inadvertently  by 
man's  activities  or  by  natural  phenomena. 

The  weather  modification  activities  of  the  Federal  Government — 
those  of  the  Congress  and  the  administrative  and  program  activities 
of  the  executive  branch  agencies — are  encompassed  in  chapter  5 ;  and 
the  findings  and  recommendations  of  major  policy  studies,  conducted 
by  or  on  behalf  of  the  Federal  Government,  are  summarized  in  chap- 
ter 6.  The  seventh,  eighth,  and  ninth  chapters  are  concerned  with 
weather  modification  activities  at  the  level  of  State  and  local  govern- 
ments, by  private  organizations,  and  in  foreign  countries,  respectively. 

111  :'<m-  Modification  Advisory  Hoard,  "A  TVS  Policy  to  Enhance  the  Atmospheric 
Environment,"  Oct.  21,  1!>77.  A  discussion  paper,  included  with  testimony  of  Harlan  Cleve- 
land, Chairman  of  the  Advisory  Hoard,  in  a  congressional  hearing:  U.S.  Congress.  House 
of  Representatives.  Committee  on  Science  and  Technology.  Subcommittee  on  the  Environ- 
ment and  the  Atmosphere.  Weather  Modification.  !).".th  Cong.,  1st  sess.,  Oct.  2(5,  1J>77, 
Washington,  D.C.,  U.S.  Government  Printing  Office,  H»77.  p.  25. 

211  Copies  of  the  current  official  position  of  the  I'.S.  Department  of  Defense  on  weather 
modification  and  of  the  draft  TT.\  convention  prohibiting  hostile  use  of  environmental 
modification,  respectively,  are  found  in  apps.  B  and  C. 


The  increasingly  important  international  problems  related  to  weath- 
er modification  are  addressed  in  chapter  10,  while  both  domestic  and 
international  legal  aspects  are  discussed  in  chapter  11.  Chapters  12 
and  13,  respectively,  contain  discussions  on  economic  and  ecological 
aspects  of  this  emerging  technology. 

The  20  appendixes  to  the  report  provide  materials  that  are  both  sup- 
plementary to  textual  discussions  in  the  13  chapters  and  intended 
to  be  valuable  sources  of  reference  data.  In  particular,  attention  is 
called  to  appendix  D,  which  contains  excerpts  dealing  with  weather 
modification  from  the  statutes  of  the  29  States  in  which  such  activities 
are  in  some  way  addressed  by  State  law,  and  to  appendix  E,  which 
provides  the  names  and  affiliations  of  individuals  within  the  50  States 
who  are  cognizant  of  weather  modification  activities  and  interests  with- 
in the  respective  States.  The  reader  is  referred  to  the  table  of  contents 
for  the  subjects  of  the  remaining  appendixes. 

Summary  or  Issues  in  Planned  Weather  Modification 

"The  issues  we  now  face  in  weather  modification  have  roots  in  the 
science  and  technology  of  the  subject,  but  no  less  importantly  in  the 
politics  of  Government  agencies  and  congressional  committees  and  in 
public  attitudes  which  grow  out  of  a  variety  of  historical,  economic, 
and  sociological  factors."  21  In  this  section  there  will  be  an  identifica- 
tion of  critical  issues  which  have  limited  development  of  weather 
modification  and  which  influence  the  ability  to  direct  weather  modifi- 
cation in  a  socially  responsible  manner.  The  categories  of  issues  do 
not  necessarily  correspond  with  the  subjects  of  succeeding  chapters 
dealing  with  various  aspects  of  weather  modification ;  rather,  they  are 
organized  to  focus  on  those  specific  areas  of  the  subject  where  there 
has  been  and  there  are  likely  to  be  problems  and  controversies  which 
impede  the  development  and  application  of  this  technology. 

The  following  sections  examine  technological,  governmental,  legal, 
economic,  social,  international,  and  ecological  issues.  Since  the  primary 
concern  of  this  report  is  with  the  intentional,  planned  use  of  weather 
modification  for  beneficial  purposes,  the  issues  summarized  are  those 
involved  with  the  development  and  use  of  this  advertent  technology. 
Issues  and  recommendations  for  further  research  in  the  area  of  inad- 
vertent weather  modification  are  included  in  chapter  4,  in  which  that 
general  subject  is  fully  discussed. 


In  a  recent  discussion  paper,  the  Weather  Modification  Advisory 
Board  summarized  the  state  of  weather  modification  by  concluding 
that  "no  one  knows  how  to  modify  the  weather  very  well,  or  on  a  very 
large  scale,  or  in  many  atmospheric  conditions  at  all.  The  first  require- 
ment of  a  national  policv  is  to  learn  more  about  the  atmosphere  it- 
self." 22  Representative  of  the  state  of  weather  modification  science 

21Fleagle.  Crutchfield,  Johnson,  and  Abdo,  "Weather  Modification  in  the  Public  Inter- 
est," 1973,  p.  15.  .  .        .  . 

22  Weather  Modification  Advisory  Board.  "A  U.S.  Policy  To  Enhance  the  Atmospheric 
Environment."  Oct.  21,  1977.  This  discussion  paper  was  included  with  the  testimony  ot 
Mr.  Harlan  Cleveland,  Chairman  of  the  Advisory  Board,  in  a  recent  congressional  hearing  : 
U.S.  Congress,  House  of  Representatives,  Committee  on  Science  and  Technology,  Subcom- 
mittee on  the  Environment  and  the  Atmosphere.  "Weather  Modification.  9oth  Cong.,  1st 
sess.  Oct.  26,  1977,  Washington,  D.C.,  U.S.  Govt.  Print.  Off.,  1977,  p.  25. 


and  technology  is  the  following  commentary  on  the  state  of  under- 
standing in  the  case  of  precipitation  enhancement,  or  rainmaking  as  it 
is  popularly  called : 

Today,  despite  the  fact  that  modern  techniques  aimed  at  artificial  stimulation 
of  rain  rest  upon  sound  physical  principles,  progress  is  still  fairly  slow.  The 
application  of  these  principles  is  complicated  by  the  overwhelming  complexity 
of  atmosheric  phenomena.  It  is  the  same  dilemna  that  meteorologists  face  when 
they  attempt  to  predict  weather.  In  both  cases,  predicting  the  evolution  of 
atmospheric  processes  is  limited  by  insufficient  knowledge  of  the  effects  produced 
by  the  fairly  well-known  interactive  mechanisms  governing  atmospheric  phenom- 
ena. Moreover,  the  temporal  and  spatial  variability  of  atmospheric  phenomena 
presents  an  additional  difficulty.  Since  any  effects  that  are  produced  by  artificial 
intervention  are  always  imposed  upon  already  active  natural  processes,  assess- 
ment of  the  consequences  becomes  even  more  difficult.23 

Grant  recognizes  the  current  progress  and  the  magnitude  of  remain- 
ing problems  when  he  says  that : 

Important^and  steady  advances  have  been  made  in  developing  technology 
for  applied  weather  modification,  but  complexity  of  the  problems  and  lack  of 
adequate  research  resources  and  commitment  retard  progress.  Advances  have 
been  made  in  training  the  needed  specialists,  in  describing  the  natural  and 
treated  cloud  systems,  and  in  developing  methodology  and  tools  for  the  necessary 
research.  Nevertheless,  further  efforts  are  required.24 

Though  it  can  be  argued  that  progress  in  the  development  of  weather 
modification  has  been  retarded  by  lack  of  commitment,  ineffective 
planning,  and  inadequate  funding,  there  are  specific  scientific  and  tech- 
nical problems  and  issues  needing  resolution  which  can  be  identified 
beyond  these  management  problems  and  the  basic  scientific  problem 
quoted  above  with  respect  to  working  with  the  atmosphere.  Particular 
technical  problems  and  issues  at  various  levels  which  continue  to  affect 
both  research  and  operational  activities  are  listed  below : 

1.  There  is  substantial  diversity  of  opinion,  even  among  informed 
scientists,  on  the  present  state  of  technology  for  specific  types  of 
weather  modification  and  their  readiness  for  application  and  with 
regard  to  weather  modification  in  general.-5 

%2.  There  are  many  who  view  weather  modification  only  as  a  drought- 
relief  measure,  expecting  water  deficits  to  be  quickly  replenished 
through  its  emergency  use;  however,  during  such  periods  weather 
modification  is  limited  by  less  frequent  opportunities ;  it  should,  in- 
stead, be  developed  and  promoted  for  its  year-round  use  along  with 
other  water  management  tools.-0 

3.  The  design  and  analysis  of  weather  modification  experiments  is 
intimately  related  to  the  meteorological  prediction  problem,  which 
needs  further  research,  since  the  evaluation  of  any  attempt  to  modify 
the  atmosphere  depends  on  a  comparison  between  some  weather  pa- 
rameter and  an  estimate  of  what  would  have  happened  naturally. 

4.  Many  of  the  problems  which  restrict  Understanding  and  predic- 
tion of  weather  modification  phenomena  stem  from  imprecise  knowl- 
edge of  fundamental  cloud  processes;  the  level  of  research  in  funda- 

2:1  Dennis,  Arnett  S.,  and  A.  Ge^in.  "Recommendations  for  Future  Research  in  Weatlier 
Modification,"  U.S.  Department  <»i"  Commerce,  National  Oceanic  and  Atmospheric  Admin- 
istration, Environmental  Research  Laboratories.  Boulder,  Colo..  November  1077.  p.  VI. 

-"Grant.  "Scientific  and  Other  Uncertainties  of  Weather  .Modification,"  1977.  p.  17. 

88  Sec  table  2,  ch.      D.  ">!>. 

-•  Silverman.  Bernard  A.,  "What  Do  We  Need  In  Weather  Modification?"  In  preprints 
of  the  Sixth  Conference  on  Planned  and  Inadvertent  Weather  .Modification,  Oct.  lO-l.'i, 
1077,  Champaign,  111.,  Boston,  American  Meteorological  Society,  1977,  p.  308. 


mental  cloud  physics  and  cloud  modeling  has  not  kept  pace  with 
weather  modification  activity.27 

5.  Progress  in  the  area  of  weather  modification  evaluation  meth- 
odology has  been  slow,  owing  to  the  complexity  of  verification  prob- 
lems and  to  inadequate  understanding  of  cloud  physics  and  dynamics. 

6.  Most  operational  weather  modification  projects,  usually  for  the 
sake  of  economy  or  in  the  anticipation  of  achieving  results  faster  and 
in  greater  abundance,  fail  to  include  a  satisfactory  means  for  project 

7.  There  are  difficulties  inherent  in  the  design  and  evaluation  of  any 
experiment  or  operation  which  is  established  to  test  the  efficacy  of 
any  weather  modification  technique,  and  such  design  requires  the 
inclusion  of  proper  statistical  methods. 

8.  In  view  of  the  highly  varying  background  of  natural  weather 
phenomena,  statistical  evaluation  of  seeding  requires  a  sufficiently 
long  experimental  period:  many  research  projects  just  barely  fail 
to  achieve  significance  and  credibility  because  of  early  termination; 
thus,  there  is  a  need  for  longer  commitment  for  such  projects,  perhaps 
5  to  10  years,  to  insure  that  meaningful  results  can  be  obtained.2S 

9.  There  is  a  need  to  develop  an  ability  to  predict  possible  adverse 
weather  effects  which  might  accompany  modification  of  specific 
weather  phenomena  :  for  example,  the  extent  to  which  hail  suppression 
or  diminishing  hurricane  winds  might  also  reduce  beneficial  precipi- 
tation, or  the  possibility  of  increasing  hailfall  or  incidence  of  light- 
ning from  efforts  to  stimulate  rainfall  from  cumulus  clouds.29 

10.  The  translation  of  cloud-seeding  technologies  demonstrated  in 
one  area  to  another  geographical  area  has  been  less  than  satisfactory; 
this  has  been  especially  so  in  the  case  of  convective  cloud  systems, 
whose  differences  are  complex  and  subtle  and  whose  classification  is 
complicated  and  sometimes  inconsistent. 

11.  There  is  increasing  evidence  that  attempts  to  modify  clouds 
in  a  prescribed  target  area  have  also  induced  changes  outside  the 
target  area,  resulting  in  the  so-called  downwind  or  extended  area 
effect :  reasons  for  this  phenomenon  and  means  for  reducing  negative 
results  need  investigation. 

1*2.  There  is  the  possibility  that  cloud  seeding  in  a  given  area  and 
during  a  given  time  period  has  led  to  residual  or  extended  time  effects 
on  weather  phenomena  in  the  target  area  beyond  those  planned  from 
the  initial  seeding. 

13.  The  conduct  of  independent  cloud-seeding  operations  in  adjacent 
locations  or  in  the  neighborhood  of  weather  modification  experiments 
may  cause  contamination  of  the  atmosphere  so  that  experimental 
results  or  estimates  of  operational  success  are  biased. 

14.  There  have  been  and  continue  to  be  conflicting  claims  as  to 
the  reliability  with  which  one  can  conduct  cloud-seeding  operations 
so  that  the  seeding  agent  is  transported  properly  from  the  dispensing 
device  to  the  clouds  or  portions  of  the  clouds  one  seeks  to  modify. 

27  Hosier.  C.  L..  "Overt  Weather  Modification.*'  Reviews  of  Geophysics  and  Space  Phys- 
ics, vol.  12.  Xo.  3,  August  1974,  p.  526. 

28  Simpson.  Joanne,  "What  Weather  Modification  Needs."  In  preprints  of  the  Sixth 
Conference  on  Planned  and  Inadvertent  Weather  Modification.  Oct.  10-13,  1977.  Cham- 
paign. 111..  Boston.  American  Meteorological  Society.  1977,  p.  306. 

29  Hosier,  "Overt  Weather  Modification,'-  1974,  p.  325. 


15.  There  is  need  to  develop,  improve,  and  evaluate  new  and  cur- 
rently used  cloud-seeding  materials  and  to  improve  systems  for  deliv- 
ery of  these  materials  into  the  clouds. 

16.  There  is  need  to  improve  the  capability  to  measure  concentra- 
tions of  background  freezing  nuclei  and  their  increase  through  seed- 
ing; there  is  poor  agreement  between  measurements  made  with  various 
ice  nucleus  counters,  and  there  is  uncertainty  that  cloud  chamber 
measurements  are  applicable  to  real  clouds.30 

IT.  In  order  to  estimate  amounts  of  fallen  precipitation  in  weather 
modification  events,  a  combination  of  weather  radar  and  raingage 
network  are  often  used;  results  from  such  measurement  systems  have 
often  been  unsatisfactory  owing  to  the  quality  of  the  radar  and  its 
calibration,  and  to  uncertainties  of  the  radar-raingage  intercalibration. 

18.  There  is  continuing  need  for  research  in  establishing  seedability 
criteria ;  that  is,  definition  of  physical  cloud  conditions  when  seeding 
will  be  effective  in  increasing  precipitation  or  in  bringing  about  some 
other  desired  weather  change. 

10.  Mathematical  models  used  to  describe  cloud  processes  or  account 
for  interaction  of  cloud  systems  and  larger  scale  weather  systems 
greatly  oversimplify  the  real  atmosphere;  therefore,  model  research 
must  be  coupled  with  field  research.31 


The  basic  problem  which  encompasses  all  governmental  weather 
modification  issues  revolves  about  the  question  of  the  respective  roles, 
if  any,  of  the  Federal,  State,  and  local  governments.  Resolution  of  this 
fundamental  question  puts  into  perspective  the  specific  issues  of  where 
m  the  several  governmental  levels,  and  to  what  extent,  should  goals  be 
set,  policy  established,  research  and/or  operations  supported,  activities 
regulated,  and  disputes  settled.  Part  of  this  basic  question  includes 
the  role  of  the  international  community,  considered  in  another  section 
on.  international  issues;32  the  transnational  character  of  weather  modi- 
fication may  one  day  dictate  the  principal  role  to  international  orga- 

Role  of  the  Federal  Government 

Because  weather  modification  cannot  be  restricted  by  State  bound- 
aries and  because  the  Federal  Government  has  responsibilities  for  re- 
source development  and  for  reduction  of  losses  from  natural  hazards, 
few  would  argue  that  the  Federal  Government  ought  not  to  have  some 
interest  and  some  purpose  in  development  and  possible  use  of  weather 
modification  technolo<rv.  The  following  broad  and  specific  issues  on 
the  role  of  the  Federal  Government  in  weather  modification  are  among 
those  which  may  be  considered  in  developing  a  Federal  policy: 

1.  Should  a  maior  policy  analysis  be  conducted  in  an  attempt  to  re- 
late weather  modification  to  the  Xatioivs  broad  goals;  that  is,  improv- 
ing human  health  and  the  qualit  v  of  life,  maintaining  national  security, 
providing  sufficient  energy  supplies,  enhancing  environmental  quality, 
and  the  production  of  food  and  fiber?  Barbara  Farhar  suggests  that 
such  a  study  has  not  been,  but  ought  to  be.  undertaken.33 

™  Fbld. 

m  Fleagle  et  al.,  "Weather  Modification  in  tUo  Public  interest."  197^.  n  St. 

n=  Sop  n.  2& 

"Farhar,  Barbara  C.  "The  Societal  Imidieations  of  Weather  Modification:  a  TCeview 
of  issues  Toward  m  National  Policy.*'  Background  paper  prepared  f«r  the  U.S.  Department 
of  Commerce  Weather  ModinVatlonAdvisory  Hoard,  Mar.  1,  1977,  p.  2. 


2.  Should  the  Federal  Government  commit  itself  to  planned  weather 
modification  as  one  of  several  priority  national  goals  ?  It  can  be  argued 
that  such  commitment  is  important  since  Federal  program  support  and 
political  attitudes  have  an  important  overall  influence  on  the  develop  - 
ment and  the  eventual  acceptance  and  application  of  this  technology. 

3.  Is  there  a  need  to  reexamine,  define,  and  facilitate  a  well-balanced, 
coordinated,  and  adequately  funded  Federal  research  and  development 
program  in  weather  modification  ?  Many  argue  that  the  current  Fed- 
eral research  program  is  fragmented  and  that  the  level  of  funding  is 

4.  Is  there  a  suitable  Federal  role  in  weather  modification  activities 
beyond  that  of  research  and  development — such  as  project  evaluation 
and  demonstration  and  operational  programs?  If  such  programs  are 
advisable,  how  can  they  be  identified,  justified,  and  established  ? 

5.  Should  the  practice  of  providing  Federal  grants  or  operational 
services  by  Federal  agencies  to  States  for  weather  modification  in  times 
of  emergency  be  reexamined,  and  should  procedures  for  providing  such 
grants  and  services  be  formalized  ?  It  has  been  suggested  that  such  as- 
sistance in  the  past  has  been  haphazard  and  has  been  provided  after  it 
was  too  late  to  be  of  any  practical  benefit. 

6.  Should  the  organizational  structure  of  the  Federal  Government 
for  weather  modification  be  reexamined  and  reorganized  ?  If  so,  what 
is  the  optimum  agency  structure  for  conducting  the  Federal  research 
program  and  other  functions  deemed  to  be  appropriate  for  the  Federal 

7.  TThat  is  the  role  of  the  Federal  Government,  if  any,  in  regulation 
of  weather  modification  activities,  including  licensing,  permitting, 
notification,  inspection,  and  reporting?  If  such  a  role  is  to  be  modified 
or  expanded,  how  should  existing  Federal  laws  and/or  regulations  be 
modified  ? 

8.  If  all  or  any  of  the  regulatory  functions  are  deemed  to  be  more  ap- 
propriate for  the  States  than  for  the  Federal  Government,  should  the 
Federal  Government  consider  mandating  minimum  standards  and 
some  uniformity  among  State  laws  and  regulations? 

9.  Should  the  Federal  Government  attempt  to  develop  a  means  ade- 
quate for  governing  the  issues  of  atmospheric  water  rights  between 
States,  on  Federal  lands,  and  between  the  United  States  and  neighbor- 
ing countries  ? 

10.  Where  federally  sponsored  research  or  possible  operational 
weather  modification  projects  occupy  the  same  locale  as  local  or 
State  projects,  with  the  possibility  of  interproject  contamination, 
should  a  policy  on  project  priorities  be  examined  and  established? 

11.  Should  the  Federal  Government  develop  a  policy  with  regard 
to  the  military  use  of  weather  modification  and  the  active  pursuit  of 
international  agreements  for  the  peaceful  uses  of  weather  modifica- 
tion? This  has  been  identified  as  perhaps  one  of  the  most  important 
areas  of  Federal  concern.34 

12.  Is  there  a  need  to  examine  and  define  the  Federal  responsibility 
for  disseminating  information  about  the  current  state  of  weather 
modication  technology  and  about  Federal  policy,  including  the  capa- 
bility for  providing  technical  assistance  to  the  States  and  to  others? 

fS*Farhar  Barbara  C.  "What  r>o°s  Weatber  Modification  Need"-  In  preprints  of  the 
Sixth  Conference  on  Planned  and  Inadvertent  Weather  Modification,  Oct.  10-13,  1977, 
Champaign.  111.,  Boston,  American  Meteorological  Society,  1977,  p.  299. 


13.  Should  there  be  a  continuing  review  of  weather  modification 
technology  capabilities  so  that  Federal  policy  can  be  informed  regard- 
ing the  readiness  of  technologies  for  export  to  foreign  nations,  with 
provision  of  technical  assistance  where  and  when  it  seems  feasible? 35 

14.  How  does  the  principle  of  cooperative  federalism  apply  to 
weather  modification  research  projects  and  possible  operations  carried 
out  within  the  States  ?  Should  planning  of  projects  with  field  activities 
in  particular  States  be  done  in  consultation  with  the  States,  and  should 
cooperation  with  the  States  through  joint  funding  and  research  efforts 
be  encouraged  ? 

15.  What  should  be  the  role  of  the  single  Federal  agency  whose 
activities  are  most  likely  to  be  affected  significantly  by  weather  modi- 
fication technology  and  whose  organization  is  best  able  to  provide 
advisory  services  to  the  States— the  U.S.  Department  of  Agriculture? 
Among  the  several  agencies  involved  in  weather  modification,  the 
Department  of  Agriculture  has  demonstrated  least  official  interest 
and  lias  not  provided  appreciable  support  to  development  of  the 

Roles  of  State  and  local  go  vernments 

State  and  local 37  governments  are  in  man}'  ways  closer  to  the 
public  than  the  Federal  Government — often  as  a  result  of  more  direct 
contact  and  personal  acquaintance  with  officials  and  through  greater 
actual  or  perceived  control  by  the  voters.  Consequently,  a  number  of 
weather  modification  functions,  for  both  reasons  of  practical  effi- 
ciency and  social  acceptance,  may  be  better  reserved  for  State  and/or 
local  implementation.  Since  weather  phenomena  and  weather  modifica- 
tion operations  cannot  be  restricted  by  State  boundaries  or  by  bound- 
aries within  States,  however,  many  functions  cannot  be  carried  out 
in  isolation.  Moreover,  because  of  the  economy  in  conducting  research 
nnd  development  on  a  common  basis — and  perhaps  performing  other 
functions  as  well — through  a  single  governmental  entity,  such  as  an 
agency  or  agencies  of  the  Federal  Government,  it  may  be  neither 
feasible  nor  wise  for  State  governments  (even  less  for  local  jurisdic- 
tions) to  carry  out  all  activities. 

Thus,  there  are  activities  which  might  best  be  reserved  for  the  States 
(and  possibly  for  local  jurisdictions  within  States),  and  those  which 
more  properly  belong  to  the  Federal  Government.  In  the  previous 
l  ist  of  issues  on  the  role  of  the  Federal  Government,  there  was  allusion 
to  a  number  of  functions  which  might,  wholly  or  in  part,  be  the  re- 
sponsibility of  either  Federal  or  State  governments;  most  of  these 
will  not  be  repeated  here.  Issues  and  problems  concerned  primarily 
with  State  and  local  government  functions  are  listed  below: 

1.  State  weather  modification  laws.  Where  they  exist,  are  nonuni- 
form in  their  requirements  and  specifications  for  licensing,  permitting, 
inspection,  reporting,  liabilities,  and  penalties  for  violations.  More- 
over, some  State  laws  and  policies  favor  weather  modification,  while 
ot  hers  oppose  1  he  technology. 

2.  Authorities  for  funding  operational  and  research  projects  with- 
in States  and  local  jurisdictions  within  States,  through  public  funds 


:"  Changnon,  "The  Federal  Role  in  Weather  Modification."  |p.  11. 

37  ,fLocal"  bere  refers  broadly  to  any  jurisdiction  below  the  State  level  :  it  could  laelucto 
cities,  townships,  counties,  groups  of  counties,  water  districts,  or  any  other  organized  area 
Operating  under  public  authority. 


or  through  special  tax  assessments,  vary  widely  and,  except  in  a  few 
States,  do  not  exist. 

3.  Decisionmaking  procedures  for  public  officials  appear  to  be  often 
lacking;  these  could  be  established  and  clarified,  especially  as  the  pos- 
sibility of  more  widespread  application  of  weather  modification  tech- 
nology approaches. 

4.  Many  public  officials,  usually  not  trained  in  scientific  and  en- 
gineering skills,  often  do  not  understand  weather  modification  tech- 
nology, its  benefits,  and  its  potential  negative  consequences.  Some 
training  of  such  officials  could  contribute  to  their  making  wise  de- 
cisions on  the  use  of  the  technology,  even  without  complete  informa- 
tion on  which  to  base  such  decisions. 

5.  Many  weather  modification  decisions  have  had  strong  political 
overtones,  with  some  legislators  and  other  public  officials  expressing 
their  views  or  casting  their  votes  allegedly  on  the  basis  of  political 
expediency  rather  than  on  the  basis  of  present  or  potential  societal 

6.  State  and  local  authorities  may  need  to  provide  for  the  education 
of  the  general  public  on  the  rudiments  of  weather  modification,  on  its 
economic  benefits  and  disbenefits.  and  on  other  societal  aspects. 

7.  To  keep  communication  channels  open,  mechanisms  such  as  pub- 
lic hearings  could  be  established  to  receive  comments,  criticisms,  and 
general  public  sentiments  on  weather  modification  projects  from  in- 
dividual citizens  and  from  various  interest  groups. 

8.  Criteria  and  mechanisms  have  not  been  established  for  compen- 
sating those  individuals  or  groups  within  States  who  might  be  eco- 
nomically injured  from  weather  modification  operations. 

9.  Questions  of  water  rights  within  States,  as  well  as  between  States, 
have  not  been  addressed  and/or  resolved  in  a  uniform  manner. 


Legal  issues  in  weather  modification  are  complex  and  unsettled. 
They  can  be  discussed  in  at  least  four  broad  categories : 

1.  Private  rights  in  the  clouds ; 

2.  Liability  for  weather  modification  ; 

3.  Interstate  legal  issues ;  and 

4.  International  legal  issues,38 

The  body  of  law  on  weather  modification  is  slight,  and  existing  case 
law  offers  few  guidelines  to  determine  these  issues.  It  is  often  neces- 
sary, therefore,  to  analogize  weather  modification  issues  to  more  set- 
tled areas  of  law  such  as  those  pertaining  to  water  distribution. 

Private  rights  in  the  clouds 

The  following  issues  regarding  private  rights  in  the  clouds  may  be 
asked : 

Are  there  any  private  rights  in  the  clouds  or  in  the  water  which 
may  be  acquired  from  them  ? 

Does  a  landowner  have  any  particular  rights  in  atmospheric 
water  ? 

Does  a  weather  modifier  have  rights  in  atmospheric  water  \ 

^Questions  on  regulation  or  control  of  weather  modification  activities  through  licensing 
and  permitting,  while  of  a  basic  legal  nature,  are  related  to  important  administrative  func- 
tions and  are  dealt  with  under  issues  concerned  with  Federal  and  State  activities. 


Some  State  statutes  reserve  the  ownership  or  right  to  use  atmospheric 
water  to  the  State.39 

There  is  no  general  statutory  determination  of  ownership  of  atmos- 
pheric water  and  there  is  no  well-developed  body  of  case  law.  Conse- 
quently, analogies  to  the  following  general  common  law  doctrines  may 
be  helpful,  but  each  has  its  own  disadvantages  when  applied  to  weather 
modification : 

1.  The  doctrine  of  natural  rights,  basically  a  protection  of  the  land- 
owner's right  to  use  his  land  in  its  natural  condition  (i.e.,  precipita- 
tion is  essential  to  use  of  the  land  as  are  air,  sunlight,  and  the  soil 

2.  The  ad  coelum  doctrine  which  states  that  whoever  owns  the  land 
ought  also  to  own  all  the  space  above  it  to  an  indefinite  extent. 

3.  The  doctrine  of  riparian  rights,  by  which  the  one  owning  land 
which  abuts  a  watercourse  may  make  reasonable  use  of  the  writer,  sub- 
ject to  similar  rights  of  others  whose  lands  abut  the  watercourse. 

4.  The  doctrine  of  appropriation,  which  gives  priority  of  right  based 
on  actual  use  of  the  water. 

5.  The  two  main  doctrines  of  ownership  in  the  case  of  oil  and  gas 
(considered,  like  water,  to  be  "fugitive  and  migratory"  substances)  ; 
that  is,  (a)  the  non-ownership  theory,  by  which  no  one  owns  the  oil  and 
gas  until  it  is  produced  and  anyone  may  capture  them  if  able  to  do  so; 
and  (b)  the  ownership-in-place  theory,  by  which  the  landowner  has  the 
same  interest  in  oil  and  gas  as  in  solid  minerals  contained  in  his  land. 

6.  The  concept  of  "developed  water,"  that  is,  water  that  would  not 
be  available  or  would  be  lost  were  it  not  for  man's  improvements. 

7.  The  concept  of  "imported  water,"  that  is,  water  brought  from  one 
watershed  to  another. 

Liability  for  weather  modification 

Issues  of  liability  for  damage  may  arise  when  drought,  flooding,  or 
other  severe  weather  phenomena  occur  following  attempts  to  modify 
the  weather.  Such  issues  include  causation  as  well  as  nuisance,  strict 
liability,  trespass,  and  negligence.  Other  issues  which  could  arise  relate 
to  pollution  of  the  air  or  water  through  introduction  of  artificial  nu- 
cleants  such  as  silver  iodide,  into  the  environment.  While  statutes  of 
10  States  discuss  weather  modification  liability,  there  is  much  varia- 
tion among  the  specific  provisions  of  the  laws  in  those  States.40 

Before  any  case  can  be  made  for  weather  modification  liability 
based  upon  causation  it  must  be  proven  that  the  adverse  weather  con- 
ditions  were  indeed  brought  about  by  the  weather  modifier,  a  very 
heavy  burden  of  proof  for  the  plaintiff.  In  fact,  the  scientific  uncer- 
tainties of  weather  modi  Heal  ion  are  such  that  no  one  has  ever  been  able 
to  establish  causation  of  damage  through  these  activities.  As  weal  her 
modification  technology  is  improved,  however,  the  specter  of  a  host  of 
liability  issues  is  expected  to  emerge  as  evidence  for  causation  becomes 
more  plausible. 

While  the  general  defense  of  the  weather  modifier  against  liability 
charges  is  that  causation  has  not  been  established,  he  may  also  use  as 
further  defense  the  arguments  based  upon  immunity,  privilege,  con- 
sent ,  and  waste. 

•  Sec  p.  4.">o,  ch.  1 1.  and  app.  n. 

M  Sec  discussion  p.  453  in  ch.  11  and  app.  D. 


Interstate  legal  issues 

When  weather  modification  activities  conducted  in  one  State  affect 
another  State  as  well,  significant  issues  may  arise.  The  following- 
problem  categories  are  examples  of  some  generally  unresolved  inter- 
state issues  in  weather  modification : 

1.  There  may  be  the  claim  that  cloud  seeding  in  one  State  has  removed 
from  the  clouds  water  which  should  have  fallen  in  a  second  State  or 
that  excessive  flooding  in  a  neighboring  State  has  resulted  from  seed- 
ing in  a  State  upwind. 

2.  Operation  of  cloud-seeding  equipment  near  the  border  in  one  State 
may  violate  local  or  State  ordinances  which  restrict  or  prohibit  weather 
modification  in  an  adjacent  State,  or  such  operations  may  conflict  with 
regulations  for  licensing  or  permitting  of  activities  within  the  bor- 
dering State. 

Some  States  have  attempted  to  resolve  these  issues  through  specific 
legislation  and  through  informal  bilateral  agreements.41  Another  ap- 
proach would  be  through  interstate  compact,  though  such  compacts  re- 
quire the  consent  of  Congress.  No  compacts  specifically  concerned  with 
weather  modification  currently  exist,  though  some  existing  compacts 
allocating  waters  in  interstate  streams  may  be  applicable  to  weather 

International  legal  issues 

Because  atmospheric  processes  operate  independent  of  national 
borders,  weather  modification  is  inherently  of  international  concern. 
International  legal  issues  have  similarities  to  domestic  interstate  activi- 
ties and  dangers.  The  following  serious  international  questions,  which 
have  arisen  in  conjunction  with  a  developing  capability  to  modify  the 
weather,  have  been  identified  by  Orfield : 42 

Do  countries  have  the  right  to  take  unilateral  action  in  all 
weather  modification  activities? 

What  liability  might  a  country  incur  for  its  weather  modifica- 
tion operations  which  [might]  destroy  life  and  property  in  a 
foreign  State? 

On  what  theory  could  and  should  that  State  base  its  claim  ? 
The  primary  international  legal  issue  regarding  weather  modifica- 
tion is  that  of  liability  for  transnational  injury  or  damage,  which  could 
conceivably  result  from  any  of  the  following  situations : 

(1)  injury  or  damage  in  another  nation  caused  by  weather 
modification  activities  executed  within  the  United  States; 

(2)  injury  or  damage  in  another  nation  caused  by  weather 
modification  activities  executed  in  that  nation  or  a  third  nation  by 
the  United  States  or  a  citizen  of  the  United  States ; 

(3)  injury  or  damage  in  another  nation  caused  by  weather 
modification  activities  executed  in  an  area  not  subject  to  the  juris- 
diction of  any  nation  (e.g.,  over  the  high  seas),  by  the  United 
States  or  a  citizen  thereof ;  and 

(4)  injury  or  damage  to  an  alien  or  an  alien's  property  within 
the  United  States  caused  by  weather  modification  activities  exe- 
cuted within  the  United  States. 

41  See  discussion  p.  457  in  ch.  11  and  app.  D. 

42  Orfield,  Michael  B..  "Weather  Genesis  and  Weather  Neutralization:  a  New  Approach 
to  Weather  Modification,"  California  Western  International  Law  Journal,  vol.  6,  no.  2, 
spring  1976,  p.  414. 

34-S57— 79  4 


Whereas  domestic  weather  modification  law  is  confused  and  unset- 
tled, international  law  in  this  area  is  barely  in  the  formative  stage.  In 
time,  ramifications  of  weather  modification  may  lead  to  major  interna- 
tionl  controversy.43 


The  potential  for  long-term  economic  gains  through  weather  modi- 
fication cannot  be  denied  ;  however,  current,  economic  analyses  are  tenu- 
ous in  view  of  present  uncertainty  of  the  technology  and  the  complex 
nature  of  attendant  legal  and  economic  problems.  Meaningful  economic 
evaluation  of  weather  modification  activities  is  thus  limited  to  special, 
localized  cases,  such  as  the  dispersal  of  cold  fog  at  airports,  where  bene- 
fit-cost ratios  greater  than  5  to  1  have  been  realized  through  savings  in 
delayed  or  diverted  traffic.  Various  estimated  costs  for  increased  pre- 
cipitation through  cloud  seeding  range  from  $1.50  to  $2.50  per  acre- 
foot  in  the  western  United  States. 

fsy/es  complicating  economic  analyses  of  weather  modification 

Costs  of  most  weather  modification  operations  are  usually  relatively 
small  and  are  normally  believed  to  be  only  a  fraction  of  the  benefits 
obtained  through  such  operations.  However,  if  all  the  benefits  and  all 
the  costs  are  considered,  benefit-cost  ratios  may  be  diminished.  While 
direct  costs  and  benefits  from  weather  modification  are  reasonably 
obvious,  indirect  costs  and  benefits  are  elusive  and  require  further  study 
of  sociological,  legal,  and  ecological  implications. 

In  analyzing  benefit-cost  ratios,  some  of  the  following  considerations 
need  to  be  examined  : 

Weather  modification  benefits  must  be  considered  in  terms  of 
the  costs  for  achieving  the  same  objectives  as  increased  precipita- 
tion, e.g.,  through  importation  of  water,  modified  use  of  agricul- 
tural chemicals,  or  introduction  of  improved  plant  strains. 

Costs  for  weather  modification  operations  are  so  low  in  compari- 
son with  other  agricultural  investments  that  farmers  may  gamble 
in  spending  the  5  to  20  cents  per  acre  for  operations  designed  to 
increase  rainfall  or  suppress  hail  in  order  to  increase  yield  per 
acre,  even  though  the  results  of  the  weather  modification  opera- 
tions may  be  doubtful. 

Atmospheric  conditions  associated  with  prolonged  droughts  are 
not  conducive  to  success  in  increasing  precipitation;  however, 
under  these  conditions,  it  is  likely  that  increased  expenditures 
may  be  made  for  operations  which  offer  little  hope  of  economic 

Increased  precipitation,  obtained  through  a  weather  modifica- 
tion program  sponsored  and  funded  by  a  group  of  farmers',  can 
also  benefit  other  farmers  who  have  not  shared  in  the  costs;  thus, 
the  benefit-cost  ratio  to  those  participating  in  the  program  is 
higher  than  it  need  be  if  all  share  in  its  costs. 

As  weather  modification  technology  develops  and  programs  be- 
come more1  sophisticated',  increased  costs  for  equipment  and  labor 
will  increase  direct  costs  to  clients:  indirect  costs  resulting  from 
increased  State  license  and  permit  fees  and  liability  insurance  for 
operators  will  probably  also  be  passed  on  to  the  customer. 

I:  s»'c  ch.  10  on  International  aspects  and  i>.  4<;s.  ch.  11;  on  International  legal  aspects  of 
wpa  i  her  modification. 


The  sophistication  of  future  programs  will  likely  incur  addi- 
tional costs  for  design,  evaluation,  and  program  information  ac- 
tivities, along  with  supporting  meteorological  prediction  services; 
these  costs  will  be  paid  from  public  funds  or  by  private  clients,  in 
either  case  reducing  the  overall  benefit-cost  ratios. 

Ultimate  costs  for  compensation  to  those  incurring  disbenefits 
from  weather  modification  operations  will  offset  overall  benefits 
and  thus  reduce  bene  fit -cost  ratios. 

Weather  modification  and  conflicting  interests 

There  are  numerous  cases  of  both  real  and  perceived  economic  losses 
which  one  or  more  sectors  of  the  public  may  suff  er  while  another  group 
is  seeking  economic  advantage  through  some  form  of  weather  modi- 
fication. Overall  benefits  from  weather  modification  are  accordingly 
reduced  when  net  gains  are  computed  from  such  instances  of  mixed 
economic  advantages  and  disadvantages.  Benefits  to  the  parties  seek- 
ing economic  gain  through  weather  modification  will  be  directly  re- 
duced at  such  time  when  mechanisms  are  established  for  compensating 
those  who  have  suffered  losses.  The  following  are  some  examples  of 
such  conflicting  situations : 

Successful  suppression  of  hail  may  be  valuable  in  reducing  crop 
damage  for  orchardists  while  other  agricultural  crops  may  suffer 
f  rom  decrease  of  rain  concomitant  with  the  hail  decrease. 

Additional  rainy  days  may  be  of  considerable  value  to  farmers 
during  their  growing  season  but  may  be  detrimental  to  the  finan- 
cial success  of  outdoor  recreational  enterprises. 

Increased  snowpack  from  orographic  cloud  seeding  may  be 
beneficial  to  agricultural  and  hydroelectric  power  interests  but 
increases  the  costs  for  maintaining  free  passage  over  highways 
and  railroads  in  mountainous  areas. 

Successful  abatement  of  winds  from  severe  storms,  such  as  those 
of  hurricanes,  may  result  in  decreased  precipitation  necessary  for 
agriculture  in  nearby  coastal  regions  or  may  redistribute  the  ad- 
verse storm  effects,  so  that  one  coastal  area  is  benefitted  at  the  ex- 
pense of  others. 


It  has  been  said  that  "weather  modification  is  a  means  toward  so- 
cially desired  ends,  not  an  end  in  itself.  It  is  one  potential  tool  in  a  set 
of  possible  societal  adjustments  to  the  vagaries  of  the  weather.  Iden- 
tifying when,  where,  and  how  to  use  this  tool,  once  it  is  scientifically 
established,  is  the  primary  need  in  weather  modification." 44  It  is  likely 
that,  in  the  final  analysis,  the  ultimate  decisions  on  whether  weather 
modification  should  and  will  be  used  in  any  given  instance  or  will  be 
adopted  more  generally  as  national  or  State  programs  depends  on 
social  acceptance  of  this  tool,  no  matter  how  well  the  tool  itself  has 
been  perfected.  That  this  is  increasingly  the  case  has  been  Suggested  by 
numerous  examples  in  recent  years.  Recently  Silverman  said : 

Weather  modification,  whether  it  he  research  or  operations,  will  not  progress 
wisely,  or  perhaps  at  all,  unless  it  is  considered  in  a  context  that  includes  everyone 

M  Fnrhar.  Barbara  C.  "What  Does  Weather  Modification  Need  ?"  In  preprints  of  the  Sixth 
Conference  on  rianr.pd  and  Inadvertent  Weather  Modification.  October  10-13,  1977.  Cham- 
paign* 111.  Boston.  American  Meteorological  Society,  1977.  p.  296. 


that  may  be  affected.  We  must  develop  and  provide  a  new  image  of  weather 

Regardless  of  net  economic  benefits,  a  program  is  hard  to  justify 
when  it  produces  obvious  social  losses  as  well  as  gains. 

Research  in  the  social  science  of  weather  modification  has  not  kept 
pace  with  the  development  of  the  technology,  slow  as  that  has  been. 
In  time,  this  failure  may  be  a  serious  constraint  on  further  develop- 
ment and  on  its  ultimate  application.  In  the  past,  organized  opposition 
has  been  very  effective  in  retarding  research  experiments  and  in  cur- 
tailing operational  cloud-seeding  programs.  Thus,  there  is  need  for  an 
expanded  effort  in  understanding  public  behavior  toward  weather 
modification  and  for  developing  educational  programs  and  effective 
decisionmaking  processes  to  insure  intelligent  public  involvement  in 
eventual  application  of  the  technology. 

Social  issues  discussed  in  this  section  are  those  which  relate  to  public 
behavior  and  public  response  to  weather  modification,  while  societal 
issues  are  generally  considered  to  include  economic,  legal,  and  other 
nontechnical  issues  as  Veil  as  the  social  ones.  These  other  aspects  of 
societal  issues  were  discussed  in  preceding  sections.  In  the  subsections 
to  follow  there  are  summaries  of  social  implications  of  weather  modifi- 
cation, the  need  for  public  education,  and  the  problem  of 

Social  factors 

It  has  been  said  that  social  factors  are  perhaps  the  most  elusive  and 
difficult  weather  modification  externalities  to  evaluate  since  such  fac- 
tors impinge  on  the  vast  and  complex  area  of  human  values  and  at- 
titudes.46 Fleagle,  et  al.,  identified  the  following  important  social 
implications  of  weather  modification,  which  would  presumably  be 
taken  into  account  in  formulation  of  policies : 47 

1.  The  individuals  and  groups  to  be  affected,  positively  or  negatively,  by  tlie 
project  must  be  defined.  An  operation  beneficial  to  one  party  may  actually  barm 
another.  Or  an  aggrieved  party  may  hold  the  operation  responsible  *  *  :::  for 
damage  *  *  *  which  might  occur  at  the  same  time  or  following  the  modification. 

2.  The  impact  of  a  contemplated  weather  modification  effort  on  the  genera! 
well-being  of  society  and  the  environment  as  a  whole  must  be  evaluated.  Con- 
sideration should  be  given  to  conservationists,  outdoor  societies,  and  other 
citizens  and  groups  representing  various  interests  who  presently  tend  to  ques- 
tion any  policies  aimed  at  changes  in  the  physical  environment.  It  is  reasonable 
and  prudent  to  assume  that,  as  weather  modification  operations  expand,  question- 
ing and  opposition  by  the  public  will  become  more  vocal. 

3.  Consideration  must  be  given  to  the  general  mode  of  human  behavior  in 
response  to  innovation.  There  are  cases  where  local  residents,  perceiving  a  cause 
and  effect  relationship  between  economic  losses  from  severe  weather  and  nearby 
weather  modification  operations,  have  continued  to  protest,  and  even  to  threaten 
violence,  after  all  operations  bave  been  suspended. 

4.  The  uniqueness  and  complexity  of  certain  weather  modification  operations 
must  be  acknowledged,  and  special  attention  should  be  given  to  their  social  and 
legal  implications.  The  cases  of  hurricanes  and  tornadoes  are  especially  perti- 
nent. Alteration  of  a  few  degrees  in  the  path  of  a  hurricane  may  result  in  its 
missing  a  certain  area  *  *  *  and  ravaging  *  *  *  instead,  a  different  one.  The  decision 
on  whether  such  an  operation  is  justified  can  reasonably  be  made  only  at  the 
highest  level,  and  would  need  to  be  based  on  the  substantial  scientific  finding 
thai  the  anticipated  damages  would  be  loss  than  those  originally  predicted  h  td 
the  hurricane  been  allowed  to  follow  its  course. 

1  b  Silverman,  Bernard  A.  "What  Do  We  Need  in  Weather  Modification?"  In  preprints  of 
tli<'  Sixth  Conference  on  Planned  and  [nadvertenl  Weather  Modification,  October  10—13, 
litTT.  Champaign,  ill..  Boston,  American  Meteorological  Society.  u»77.  p.  310. 

ia  Flengle,  Crutchfleld,  Johnson,  and  Abdo.  "Weather  Modification  in  the  Public  Interest." 
1074.  p.  :',7-38. 

*•  Ibid.,  p.  38-40. 


5.  Attention  must  be  given  to  alternatives  in  considering  a  given  weather 
modification  proposal.  The  public  may  prefer  some  other  solution  to  an  attempt 
at  weather  tampering  which  may  be  regarded  as  predictable  and  risky.  Further- 
more, alternative  policies  may  tend  to  be  comfortable  extensions  of  existing 
policies,  or  improvements  on  them,  thus  avoiding  the  public  suspicion  of  inno- 
vation. In  an  area  such  as  weather  modification,  where  so  many  uncertainties 
exist,  and  where  the  determination  or  assigning  of  liability  and  responsibility 
are  far  from  having  been  perfected,  public  opposition  will  surely  be  aroused. 
Any  alternative  plan  or  combination  of  plans  will  have  its  own  social  effects, 
however,  and  it  is  the  overall  impact  of  an  alternative  plan  and  the  adverse 
effects  of  not  carrying  out  such  a  plan  which,  in  the  final  analysis,  should  guide 
decisions  on  alternative  action. 

6.  Finally,  it  is  important  to  recognize  that  the  benefits  from  a  weather  modi- 
fication program  may  depend  upon  the  ability  and  readiness  of  individuals 
to  change  their  modes  of  activity.  The  history  of  agricultural  extension  work 
in  the  United  States  suggests  that  this  can  be  done  successfully,  but  only  with 
some  time  lag,  and  at  a  substantial  cost.  Social  research  studies  suggest  that 
public  perception  of  flood,  earthquake,  and  storm  hazards  is  astonishingly  casual. 

Need  for  public  education  on  weather  modification 

The  previous  listing  of  social  implications  of  weather  modification 
was  significantly  replete  with  issues  derived  from  basic  human  atti- 
tudes. To  a  large  extent  these  attitudes  have  their  origin  in  lack  of  in- 
formation, misconceptions,  and  even  concerted  efforts  to  misinform  by 
organized  groups  which  are  antagonistic  to  weather  modification.  As 
capabilities  to  modify  weather  expand  and  applications  are  more  wide- 
spread, it  would  seem  probable  that  this  information  gap  would  also 
widen  if  there  are  no  explicit  attempts  to  remedy  the  situation.  "At  the 
very  least,"  according  to  Fleagle,  et  al.,  "a  large-scale  continuing  pro- 
gram of  education  (and  perhaps  some  compulsion)  will  be  required  if 
the  potential  social  gains  from  weather  modification  are  to  be  realized 
in  fact,"  48  Whether  such  educational  programs  are  mounted  by  the 
States  or  by  some  agency  of  the  Federal  Government  is  an  issue  of 
jurisdiction  and  would  likely  depend  on  whether  the  Federal  Govern- 
ment or  the  States  has  eventual  responsibility  for  management  of  op- 
erational weather  modification  programs.  Information  might  also  be 
provided  privately  by  consumer  groups,  professional  organizations, 
the  Aveather  modification  industry,  or  the  media. 

It  is  likely  that  educational  programs  would  be  most  effective  if  a 
variety  of  practical  approaches  are  employed,  including  use  of  the 
news  media,  publication  of  pamphlets  at  a  semitechnical  level,  semi- 
nars and  hearings,  and  even  formal  classes.  Probably  the  latter  cate- 
gories would  be  most  appropriate  for  civic  groups,  Government  offi- 
cials, businessmen,  or  other  interests  who  are  likely  to  be  directly 
affected  by  contemplated  operations. 

The  following  list  of  situations  are  examples  of  public  lack  of  under- 
standing which  could,  at  least  in  part,  be  remedied  through  proper 
educational  approaches : 

There  is  much  apprehension  over  claims  of  potential  d^rger  of  a 
long-lasting  nature  on  climate,  which  could  supposedly  result 
from  both  inadvertent  and  planned  modification  of  the  weather, 
with  little  insight  to  distinguish  between  the  causes  and  the  scales 
of  the  effects. 

There  have  been  extravagant  claims,  propagated  through  ig- 
norance or  by  deliberate  distortion  by  antagonistic  groups,  about 

48  Ibid.,  p.  40. 


the  damaging  effects  of  cloud  seeding  on  ecological  systems,  human 
lien  1th.  and  air  and  water  quality. 

The  controversies  between  opposing  groups  of  scientists  on  the 
efficacy  of  weather  modification  technologies  and  between  scien- 
tists and  commercial  operators  on  the  readiness  of  these  technolo- 
gies for  application  has  engendered  a  mood  of  skepticism  and 
even  mistrust  of  weather  modification  on  the  part  of  a  public 
which  is  largely  uninformed  on  technical  matters. 

The  public  has  often  been  misinformed  by  popular  news  media, 
whose  reporters  seek  to  exploit  the  spectacular  in  popular  weather 
modification  "stories"  and  who,  themselves  usually  uninformed  in 
technical  aspects  of  the  subject,  tend  to  oversimplify  and  distort 
the  facts  associated  with  a  rather  complex  science  and  technology. 

There  has  been  an  organized  effort  on  the  part  of  groups  opposed 
to  weather  modification  to  mount  an  educational  program  which 
runs  counter  to  the  objectives  of  informing  the  public  about  the 
potential  benefits  of  a  socially  acceptable  technology  of  weather 

Portions  of  the  public  have  acquired  a  negative  impression  that 
meteorologists  and  Government  officials  concerned  with  weather 
modification  are  irresponsible  as  a  result  of  past  use.  or  perceived 
present  and  future  use.  of  the  technology  as  a  weapon  of  war. 

Lack  of  information  to  the  public  has  sometimes  resulted  in 
citizen  anger  when  it  is  discovered  that  a  seeding  project  has  been 
going  on  in  their  area  for  some  time  without  their  having  been 
informed  of  it. 


"The  nature  of  wenther  processes  and  the  current  knowledge  about 
them  require  that  most  human  decisions  as  to  weather  modification 
must  be  made  in  the  face  of  uncertainty.  This  imposes  special  re- 
straints on  public  agencies  and  it  increases  the  difficulty  of  predict- 
ing how  individual  farmers,  manufacturers,  and  others  who  are 
directly  affected  by  weather  would  respond  to  changes  in  leather 
Characteristics.5' 49  The  situation  since  1965  when  this  statement  was 
made  has  changed  little  with  resrard  to  predictability  of  weather 
processes  and  their  modification.  There  has  also  been  little  progress 
toward  developing  decisionmaking  processes  which  can  be  applied, 
should  the  need  arise,  on  whether  or  not  weather  modification  should 
be  emploved. 

A  number  of  studies  on  social  attitudes  indicate  that  the  preference 
of  most  cit  izens  is  that  decisionmaking  in  such  areas  as  use  or  restraint 
from  use  of  weather  modification  should  be  at  the  local  level.  owim>- 
to  the  feeling  that  citizens'  rights  and  property  are  best  protected 
when  decisions  are  made  bv  officials  over  whom  they  have  the  most 
direct;  control.  Farhar  savs  that  evidence  suggests  that  one  important 
condition  for  public  acceptance  of  weather  modification  technology 
is  public  involvement  in  the  decision  process,  especially  in  civic 
derisions.™  Procedures  must  then  be  developed  for  enabling  {peal 

49  Special  Commission  on  Wcnther  Modification.  "Weather  and  Climate  Modification." 
NRF  or,     irto.~.  p  uc. 

»  F.-irlisir.  Bar  nun)  P.  "The  Pnldie  Derides  Al<ont  Weather  Modification."'  Environment 

and  Behavior,  vol.  9.  No.  September  1 077.  p.  .".07. 


officials,  probably  not  technically  trained,  to  make  such  decisions 
intelligently.  Such  decisions  must  be  based  both  on  information 
received  from  Federal  or  State  teclmical  advisers  and  on  the  opinions 
of  local  citizens  and  interest  groups. 


International  agreements  regarding  weather  modification  experi- 
ments and  operations  have  been  very  limited.  There  exists  a  United 
States-Canada  agreement,  which  requires  consultation  and  notifica- 
tion of  the  other  country  when  there  is  the  possibility  that  weather 
modification  activities  of  one  country  could  affect  areas  across  the 
border.51  Earlier  understandings  were  reached  between  the  United 
States  and  Canada  concerning  experiments  over  the  Great  Lakes  and 
with  the  IJnited  Kingdom  in  connection  with  hurricane  modification 
research  in  the  Atlantic.52  Recent  attempts  to  reach  agreement  with 
the  Governments  of  Japan  and  the  People's  Republic  of  China  for 
U.S.  experiments  in  the  Far  East  on  modification  of  typhoons  were 
unsuccessful,  though  such  research  was  encouraged  by  the  Philip- 
pines. There  is  current  intention  to  reach  an  agreement  with  Mexico 
on  hurricane  research  in  the  eastern  Pacific  off  that  nation's  coast. 

During  1976,  25  nations  reported  to  the  World  Meteorological  Orga- 
nization that  they  had  conducted  weather  modification  activities.53 
There  have  been  two  principal  international  activities,  dealing  with 
somewhat  different  aspects  of  weather  modification,  in  recent  years. 
One  of  these  is  the  preparation  and  design  of  a  cooperative  experi- 
ment under  the  auspices  of  the  World  Meteorological  Organization, 
called  the  Precipitation  Enhancement  Experiment  (PEP)  ;  while  the 
other  is  the  development  of  a  convention  by  the  United  Nations  on 
the  prohibition  of  hostile  use  of  environmental  modification.54 

The  following  international  considerations  on  research  and  opera- 
tional weather  modification  activities  can  be  identified : 

1.  There  is  a  common  perception  of  a  need  to  insure  that  the  current 
high  level  of  cooperation  which  exists  in  the  international  community 
with  regard  to  more  general  meteorological  research  and  weather  re- 
porting will  be  extended  to  development  and  peaceful  uses  of  planned 
weather  modification. 

2.  There  is  now  no  body  of  international  law  which  can  be  applied  to 
the  potentially  serious  international  questions  of  weather  modification, 
such  as  liability  or  ownership  of  atmospheric  water  resources.55 

3.  Past  use  by  the  United  States,  and  speculated  current  or  future 
use  by  various  countries,  of  weather  modification  as  a  weapon  have 
raised  suspicions  as  to  the  possible  intent  in  developing  advertent 
weather  modification  technology. 

4.  There  have  been  charges  that  weather  modification  research  activi- 
ties were  used  to  divert  severe  weather  conditions  away  from  the 

r,t  The  United  States-Canada  agreement  on  weather  modification  is  reproduced  in  nop.  F. 

52  Taubenfeld,  Howard  J.,  "National  Weather  Modification  Policy  Act  of  1976  ;  Interna- 
tional Agreements."  Background  paper  for  use  of  the  U.S.  Department  of  Commerce 
Weather  Modification  Advisory  Board,  March  1977,  p.  13. 

53  See  table  1,  ch.  9,  p.  409. 

54  These  activities  and  other  international  aspects  of  weather  modification  are  discussed 
in  ch.  10. 

55  See  previous  section  on  legal  issues,  p.  17. 


United  States  at  the  expense  of  other  countries  or  that  such  activities 
have  resulted  in  damage  to  the  environment  in  those  countries.56 

5.  As  in  domestic  research  projects,  there  are  allegations  of  insuffi- 
cient funding  over  periods  of  time  too  short  to  achieve  significant 
results  in  the  case  of  internationally  sponsored  experiments;  in  par- 
ticular, many  scientists  feel  that  a  means  should  be  devised  to  insure 
that  the  planned  Precipitation  Enhancement  Project  (PEP)  receives 
adequate  continuous  support. 

6.  Other  nations  should  be  consulted  with  regard  to  any  planned 
weather  modification  activities  by  the  United  States  which  might  con- 
ceivably affect,  or  be  perceived  to  affect,  those  countries. 


The  body  of  research  on  ecological  effects  of  weather  modification 
is  limited  but  significantly  greater  than  it  was  a  decade  ago.  It  is 
still  true  that  much  remains  unknown  about  ecological  effects  of 
changes  to  weather  and  climate. 

Economically  significant  weather  modification  will  always  have  an 
eventual  ecological  effect,  although  appearance  of  that  effect  may  be 
hidden  or  delayed  by  system  resilience  and/or  confused  by  system 
complexity.  It  may  never  be  possible  to  predict  well  the  ecological 
effects  of  weather  modification;  however,  the  more  precisely  the 
weather  modifier  can  specify  the  effects  his  activities  will  produce  in 
terms  of  average  percentage  change  in  precipitation  (or  other  vari- 
ables), expected  seasonal  distribution  of  the  induced  change,  expected 
year-to-year  distribution  of  the  change,  and  changes  in  relative  form 
of  precipitation,  the  more  precise  can  be  the  ecologist's  prediction  of 
possible  ecological  effects. 

Ecological  effects  will  result  from  moderate  weather-related  shifts 
in  rates  of  reproduction,  growth,  and  mortality  of  plants  and  animals; 
they  will  rarely  be  sudden  or  catastrophic.  Accordingly,  weather  modi- 
fied ions  which  occur  with  regularly  over  time  are  the  ones  to  which 
biological  communities  will  react.  Adjustments  of  plant  and  animal 
communities  will  usually  occur  more  slowly  in  regions  of  highly  vari- 
able weather  than  in  those  with  more  uniform  conditions.  Deliberate 
weather  modification  is  likely  to  have  greater  ecological  impact  in 
semiarid  systems  and  less  impact  in  humid  ones.  Since  precipitation 
augmentation,  for  example,  would  have  the  greatest  potential  for  eco- 
nomic value  and  is,  therefore,  likely  to  have  its  greatest  potential  ap- 
plication in  such  areas,  the  ecological  impacts  in  transition  areas  will 
be  of  particular  concern. 

Although  widespread  cloud  seeding  could  result  in  local,  temporary 
increases  in  concentrations  of  silver  (from  the  most  commonly  used 
seeding  agent,  silver  iodide),  approaching  the  natural  quantities  in 
surface  waters,  the  exchange  rates  would  probably  be  an  order  of 
magnitude  Lower  than  the  natural  rates.  Even  in  localized  areas  of 
precipital  ion  management,  it  appears  I  hat  exchange  rates  will  be  many 
orders  of  magnitude  smaller  than  those  adversely  affecting  plants  and 
soils.  Further  research  is  required,  however,  especially  as  other  poten- 
tial seeding  agents  are  introduced. 

m  por  example  tbere  were  charges  that  attempts  to  mitigate  severe  effects  of  Hurricane 
Fifl  in  15>75  caused  devastat  ion  to  Honduras.  :i  charge  which  the  United  Nt;ites  officially 
denied,  since  no  hurricanes  had  been  seeded  under  Project  Stormfury  since  1971. 



(By  Robert  E.  Morrison,  Specialist  in  Earth  Sciences,  Science  Policy  Research 
Division,  Congressional  Research  Service) 


The  history  of  the  desire  to  control  the  weather  can  be  traced  to 
antiquity.  Throughout  the  ages  man  has  sought  to  alleviate  droughts  or 
to  allay  other  severe  weather  conditions  which  have  adversely  affected 
him  by  means  of  magic,  supplication,  pseudoscientific  procedures  such 
as  creating  noises,  and  the  more  on  less  scientifically  based  techniques 
of  recent  times. 

The  expansion  in  research  and  operational  weather  modification 
projects  has  increased  dramatically  since  World  War  II;  nevertheless, 
activities  predating  this  period  are  of  interest  and  have  also  provided 
the  roots  for  many  of  the  developments  of  the  "modern"  period.  In  a 
1966  reprt  for  the  Congress  on  weather  modification,  Lawton  Hart- 
man  stated  three  reasons  why  a  review  of  the  history  of  the  subject 
can  be  valuable:  (1)  Weather  modification  is  considerably  older  than 
is  commonly  recognized,  and  failure  to  consider  this  fact  can  lead  to  a 
distorted  view  of  current  problems  and  progress.  (2)  Weather  modi- 
fication has  not  developed  as  an  isolated  and  independent  field  of  re- 
search, but  for  over  a  century  has  been  parallel  to  and  related  to 
progress  in  understanding  weather  processes  generally.  (3)  Earlier 
experiences  in  weather  modification  may  not  have  been  very  different 
from  contemporary  experiences  in  such  matters  as  experimental  de- 
sign, evaluation  of  results,  partially  successful  projects,  and  efforts  to 
base  experiments  on  established  scientific  principles.1 

Hartman  found  that  the  history  of  weather  modification  can  be 
conveniently  divided  into  five  partially  overlapping  periods.2  He  refers 
to  these  as  (1)  a  prescientific  period  (prior  to  about  1839);  (2)  an 
early  scientific  period  (extending  approximately  from  1839  through 
1891)  ;  (3)  a  period  during  which  elements  of  the  scientific  framework 
were  established  (from  about  1875  to  1933)  ;  (4)  the  period  of  the 
early  cloud-seeding  experiments  (1921  to  1946)  ;  and  (5)  the  modern 
period,  beginning  with  the  work  of  Langmuir,  Schaefer,  and  Vonne- 
gut  (since  1946).  This  same  organization  is  adopted  in  discussions 
below ;  however,  the  four  earlier  periods  are  collected  into  one  section, 
while  the  more  significant  history  of  the  extensive  activities  of  the 
post-1946  period  are  treated  separately. 

1  Hartman,  Lawton  M.,  "History  of  Weather  Modification. "  In  U.S.  Congress,  Senate 
Committee  on  Commerce  "Weather  Modification  and  Control."  Washington.  D.C  U.S. 
Government  Printing  Oflice,  1966  (89th  Cong.,  2d  sess..  Senate  Rept.  No.  1139:  prepared 
by  the  Legislative  Reference  Service,  the  Library  of  Congress,  at  the  request  of  Warren  G. 
Maemn«on) ,  p.  11. 

2  Ibid. 



History  or  Weather  Modification  Prior  to  1946 


From  ancient  times  through  the  early  19th  century,  and  even  since, 
there  have  been  reported  observations  which  led  many  to  believe  that 
rainfall  could  be  induced  from  such  phenomena  as  great  noises  and 
extensive  fires.  Plutarch  is  reported  to  have  stated,  "It  is  a  matter  of 
current  observation  that  extraordinary  rains  pretty  generally  fall 
after  great  battles/' 3  Following  the  invention  of  gunpowder,  the  fre- 
quency of  such  claims  and  the  conviction  of  those  espousing  this 
hypothesis  increased  greatly.  Many  cases  were  cited  where  rain  fell 
shortly  after  large  battles,  A  practical  use  of  this  phenomenon  was  re- 
ported to  have  occurred  in  the  memoirs  of  Benvenuto  Cellini  when,  in 
1539  on  the  occasion  of  a  procession  in  Rome,  he  averted  an  impending 
rainstorm  by  firing  artillery  in  the  direction  of  the  clouds,  "which  had 
already  begun  to  drop  their  moisture."  4 

William  Humphreys jDOsed  a  plausible  explanation  for  the  appar- 
ently high  correlation  between  such  weather  events  and  preceding 
battles.  He  noted  that  plans  were  usually  made  and  battles  fought  in 
good  weather,  so  that  after  the  battle  in  the  temperate  regions  of 
Europe  or  North  America,  rain  will  often  occur  in  accordance  with 
the  natural  3-  to  5-day  periodicity  for  such  events.5  Even  in  modern 
times  there  was  the  conviction  that  local  and  global  weather  had  been 
adversely  affected  after  the  explosion  of  the  first  nuclear  weapons  and 
the  various  subsequent  tests  in  the  Pacific  and  elsewhere.0  Despite 
statements  of  the  U.S.  Weather  Bureau  and  others  pointing  out  the 
fallacious  reasoning,  such  notions  became  widespread  and  persistent.7 

In  addition  to  these  somewhat  rational  though  unscientific  obser- 
vations, many  of  which  were  accompanied  by  testimony  of  reliable 
witnesses,  there  had  been,  and  there  still  exist  in  some  primitive  cul- 
tures, superstitions  and  magical  practices  that  accompany  weather 
phenomena  and  attempts  to  induce  changes  to  the  weather.  Daniel 
Halacy  relates  a  number  of  such  superstitiouslike  procedures  which 
have  been  invoked  in  attempts  to  bring  rain  to  crops  during  a  drought 
or  to  change  the1  weather  in  some  other  way  so  as  to  be  of  particular 
benefit  to  man : 8 

Primitive  rainmakers  would  often  use  various  intuitive  gestures,  such  as 
sprinkling  water  on  the  soil  that  they  wanted  the  heavens  to  douse,  Mowing 
mouthfuls  of  water  into  the  air  like  rain  or  mist,  hammering  on  drums  to  inu- 
la re  thunder,  or  throwing  firebrands  into  the  air  to  simulate  lightning. 

Women  would  carry  water  at  night  to  the  field  and  pour  it  out  to  coax  the 
skies  to  do  likewise. 

American  Indians  blew  water  from  special  pipes  in  imitation  of  the  rainfall. 

It  was  believed  that  frogs  came  down  in  the  rain  because  many  were  seen 
following  rain  :  therefore,  frogs  were  hung  from  trees  so  that  the  heavens  would 
pour  down  rain  upon  them. 

Sometimes  children  were  buried  up  to  their  necks  in  the  parched  ground  and 
then  cried  for  rain,  their  tears  providing  the  imitative  magic. 

Ward,  R.  !>«•  <\.  "Artificial  Rain  :  a  Review  of  the  Subject  to  the  Close  of  lSSft."  Amor- 
lean  Meteorological  Journal;  vol.  s.  May  1891-Aprtl  *S92,  p.  484. 
*  Ibid.,  n.  408. 

s  Humphreys.  William  -1  .  "Rain  Making  and  Other  Weather  Vagaries."  Baltimore,  The 
Williams  and  Wilkins  Co..  11*20.  p.  31, 

"Byers,  Horace  i:..   'History  of  Weather  Modification."  In  Wilnot  N.  Hess  (editor), 
"Weather  and  Climate  Modification,"  New  York.  Wiley,  1!)74,  p.  4. 
~  T'.id 

«  Halacy,  Daniel  S.,  Jr.,  "The  Weather  Changers,"  New  York.  Harper  &  Row.  1908.  pp. 


In  China,  huge  paper  dragons  were  part  of  religious  festivals  to  bring  rain; 
if- drought  persisted,  the  dragon  was  angrily  torn  to  bits. 

North  American  Indians  roasted  young  women  from  enemy  tribes  over  a  slow 
fire,  then  killed  them  with  arrows  before  eating  their  hearts  and  burying  their 
remains  in  the  fields  they  wanted  irrigated  with  rainfall. 

Scottish  witches  conjured  up  the  wind  by  beating  a  stone  three  times  with  a 
rag  dipped  in  water,  among  intonations  like  those  of  characters  in  a  Shake- 
spearean play. 

New  Guinea  natives  used  wind  stones  upon  which  they  tapped  with  a  stick, 
the  force  of  the  blow  bringing  anything  from  a  zephyr  to  a  hurricane. 

Pregnant  women  in  Greenland  were  thought  to  be  able  to  go  outdoors,  take  a 
breath,  and  exhale  it  indoors  to  calm  a  storm. 

In  Scandinavian  countries  witches  sold  knotted  bits  of  string  and  cloth  which, 
supposedly,  contained  the  wind ;  untying  one  knot  at  sea  would  produce  a  mod- 
erate wind,  two  a  gale,  and  three  a  violent  storm. 

Australian  bushmen  thought  that  they  could  delay  the  Sun  by  putting  a  clod 
of  dirt  in  the  fork  of  a  tree  at  just  the  height  of  the  Sun,  or  hasten  its  departure 
by  blowing  sand  after  it. 

Bells  have  been  thought  to  prevent  hail,  lightning,  and  windstorms,  and  some- 
times they  are  still  rung  today  for  this  purpose. 


James  P.  Espy  was  a  19th  century  American  meteorologist  known 
especially  for  his  development  of  a  theon^  of  storms  based  on  convec- 
tion. Recognizing  that  a  necessary  condition  for  rainfall  is  the 
formation  of  clouds  by  condensation  of  water  vapor  from  rising  air, 
Espy  considered  that  rain  could  well  be  induced  artificially  when  air 
is  forced  to  rise  as  a  result  of  great  fires,  reviving  a  belief  of  the  pre- 
.scientific  era  but  using  scientific  rationale.  In  the  National  Gazette  in 
Philadelphia  of  April  5, 1839,  he  said  : 

From  principles  here  established  by  experiment,  and  afterward  confirmed  by 
observation,  it  follows,  that  if  a  large  body  of  air  is  made  to  ascend  in  a  column, 
a  large  cloud  will  be  generated  and  that  that  cloud  will  contain  in  itself  a  self- 
sustaining  power,  which  may  move  from  the  place  over  which  it  was  formed,  and 
cause  the  air  over  which  it  passes,  to  rise  up  into  it,  and  thus  form  more  cloud 
and  rain,  until  the  rain  may  become  more  general.8 

If  these  principles  are  just,  when  the  air  is  in  a  favorable  state,  the  bursting 
out  of  a  volcano  ought  to  produce  rain ;  and  such  is  known  to  be  the  fact ;  and 
I  have  abundant  documents  in  my  possession  to  prove  it. 

So,  under  very  favorable  conditions,  the  bursting  out  of  great  fires  ought  to 
produce  rain ;  and  I  have  many  facts  in  my  possession  rendering  it  highly 
probable,  if  not  certain,  that  great  rains  have  sometimes  been  produced  by  great 

Later  in  the  same  article  Espy  stated  that : 

From  these  remarkable  facts  above,  I  think  it  will  be  acknowledged  that  there 
is  some  connection  between  great  fires  and  rains  other  than  mere  coincidence. 
But  now.  when  it  is  demonstrated  by  the  most  decisive  evidence,  the  evidence 
of  experiment,  that  air,  in  ascending  into  the  atmosphere  in  a  column,  as  it  must 
do  over  a  great  fire,  will  cool  by  diminished  pressure,  so  much  that  it  will  begin 
to  condense  its  vapor  into  cloud.11 

Espy  postulated  three  mechanisms  which  could  prevent  great  fires 
from  providing  rain  at  all  times  when  they  occur:  (1)  If  there  is  a 
current  of  air  at  some  height,  it  sweeps  away  the  uprushing  current 
of  air;  (2)  the  dew-point  may  be  too  low  to  produce  rain  at  all:  and 
(3)  there  may  be  an  upper  stratum  of  air  so  light  that  the  rising 

9  Espy.  Tames  P..  "Artificial  Rains."  National  Gazette.  Philadelphia.  Apr.  5,  lSf!9.  Re- 
printed in  James  P.  Espy,  "Philosophy  of  Storms,"  Boston.  Little  &  Brown.  1841.  pd. 

10  Ibid.,  p.  494. 

11  Ibid.,  p.  496. 


column  may  not  be  able  to  rise  far  enough  into  it  to  cause  rain.12  He 
proposed  an  experiment  in  which  he  would  set  fire  to  a  "large  mass 
of  combustibles,"  which  would  be  ready  for  the  right  circumstances 
and  at  a  time  of  drought.  He  added :  "Soon  after  the  fire  commences, 
I  will  expect  to  see  clouds  begin  to  form  *  *  *.  I  will  expect  to  see 
this  cloud  rapidly  increase  in  size,  if  its  top  is  not  swept  off  by  a 
current  of  air  at  a  considerable  distance  abov^e  the  Earth,  until  it 
becomes  so  lofty  as  to  rain.'-  13 

For  over  a  decade  Espy  served  as  an  adviser  to  the  Congress  on 
meteorological  problems.  He  proposed  in  1850  what  is  perhaps  the  first 
Fedora!  project  for  large-scale  weather  modification.  His  plan  included 
amassing  large  quantities  of  timber  in  the  Western  States  along  a 
600-  to  700-mile  north-south  line,  to  be  set  on  fire  simultaneously  at 
regular  T-day  intervals.  He  believed  that  this  fire  could  have  started 
a  "rain  of  great  length"  traveling  toward  the  East,  not  breaking  up 
until  reaching  "far  over  the  Atlantic  Ocean;  that  it  will  rain  over 
the  whole  country  east^of  the  place  of  beginning."  The  cost  of  this 
experiment  would  "not  amount  to  half  a  cent  a  year  to  each  individual 
in  the  United  States."  14  Congress  did  not  endorse  the  proposal  for 
reasons  which  are  unknown:  however.  Fleagle  speculates  that  perhaps 
this  failure  was  due  to  the  fact  that  Congress  had  not  yet  accustomed 
itself  to  appropriating  funds  for  scientific  enterprises.15 

There  was  continuing  controversy  over  whether  or  not  fire  could 
cause  increased  rainfall.  In  an  article  which  appeared  in  Nature  in 
1871,  J.  K.  Laughton  stated  that,  "The  idea  that  large  fires  do,  in  some 
way,  bring  on  rain,  is  very  old;  but  it  was,  I  believe,  for  the  first  time 
stated  as  a  fact  and  explained  on  scientific  grounds  by  the  late  Pro- 
fessor Espy."  10  Laughton  cited  instances  where  burning  brush  in  hot, 
dry  weather  did  not  result  in  any  rainfall,  and  he  concluded  that : 

Large  fires,  explosions,  battles,  and  earthquakes  do  tend  to  cause  atmospheric 
disturbance,  and  especially  to  induce  a  fall  of  rain  ;  but  that  for  the  tendency  to 
produce  effect,  it  is  necessary  that  other  conditions  should  be  suitable.  With 
regard  to  storms  said  to  have  been  caused  by  some  of  these  agencies,  the  evidence 
is  still  more  unsatisfactory  ;  and,  in  our  present  ignorance  of  the  cause  of  storms 
generally,  is  quite  insufficient  to  compel  us  to  attribute  any  one  particular  gale, 
extending  probably  over  a  wide  area,  to  some  very  limited  and  comparatively 
insignificant  disturbance.17 

The  1871  Chicago  fire  also  aroused  interest,  many  believing  that  the 
fire  was  stopped  by  the  rainfall  which  it  had  initiated.  Ward  cites  a 
telegram  of  the  time  sent  to  London  which  read  : 

This  fire  was  chiefly  checked  on  the  third  or  fourth  day  by  the  heavy  and  con- 
tinuous downpour  of  rain,  which  it  is  conjectured  is  partly  due  to  the  great  atmos- 
pheric disturbances  which  such  an  extensive  lire  would  cause,  especially  wben  we 
are  told  that  the  season  just  previous  to  the  outbreak  of  the  fire  had  been  par- 
ticularly dry." 

u  Ibid. 

1  ■  I  'id.,  p.  400. 

«  Espy,  James  P.,  "Second  Reporl  on  Meteorology  to  the  Secretary  of  the  Navy."  U.S. 
Senate.  Executive  Doctlmetats;  No.  89,  vol.  11,  ."{1st  Cong.,  1st  Bess.  Washington,  Wm.  M 
Belt  1850.  p.  20. 

us  Fleagle.  Robert  O..  "Background  and  Present  status  of  Weather  Modification."  In 
Robert  (i.  Flea  pie  (editor).  "Weather  Modification:  Science  and  Public  Policy."  University 
of  w  ah  inert  on  Press,  Seattle  1968,  p.  7. 

"'  Lautrhton.  J  K.,  "Can  Weather  lie  Influenced  bv  Artificial  Means?"  Nature,  Feb.  10. 
1871  i.  :•(»(; 

17  Ibid.,  p.  307. 

«  Reported  in  Ward.  "Artificial  Rain  :  a  Review  of  the  Subject  to  the  Close  of  1889,"  1*02. 
pp.  480-400. 


On  the  other  hand,  Prof.  I.  A.  Lapham,  speaking  of  the  Chicago  fire, 
contradicted  the  previous  account,  saying : 

During  all  this  time — 24  hours  of  conflagration — no  rain  was  seen  to  fall,  nor 
did  any  rain  fall  until  4  o'clock  the  next  morning ;  and  this  was  not  a  very  con- 
siderable downpour,  but  only  a  gentle  rain,  that  extended  over  a  large  district  of 
country,  differing  in  no  respect  from  the  usual  rains.  It  was  not  until  4  days 
afterward  that  anything  like  a  heavy  rain  occurred.  It  is,  therefore,  quite  certain 
that  this  case  cannot  be  referred  to  as  an  example  of  the  production  of  rain  by  a 
great  fire.19 

Lapham  goes  on  to  say  that,  "The  case  neither  confirms  nor  dis- 
proves the  Espian  theory,  and  we  may  still  believe  the  well-authenti- 
cated cases  where,  under  favorable  circumstances  of  very  moist  air  and 
absence  of  wind,  rain  has  been  produced  by  very  large  fires."  20 

Prof.  John  Trowbridge  of  Harvard  reported  in  1872  on  his  experi- 
ments in  which  he  investigated  the  influence  of  flares  on  atmospheric 
electricity.  Noting  that  the  normal  atmospheric  state  is  positive  and 
that  clearing  weather  is  often  preceded  by  a  change  from  negative  to 
positive  charge,  he  suggested  that  perhaps  large  fires  may  influence  the 
production  of  rain  by  changing  the  electrical  state  of  the  atmosphere, 
since,  in  his  tests,  his  flame  tended  "to  reduce  the  positive  charge  of 
electricity  which  generally  characterizes  the  air  of  fine  weather."  21  He 
concluded  by  saying:  "The  state  of  our  knowledge,  however,  in  regard 
to  the  part  that  electricity  plays  in  atmospheric  changes  is  very  meager. 
The  question  of  the  truth  of  the  popular  belief  that  great  fires  are  fol- 
lowed by  rain  still  remains  unanswered."  22 

Meanwhile,  H.  C.  Russel,  president  of  the  Royal  Society  of  South 
Wales  and  government  astronomer,  attempted  to  dispel  the  ideas  that 
both  cannonading  and  great  fires  could  be  used  to  produce  rain.  He 
hypothesized  that,  if  fire  were  to  have  such  an  effect,  rain  should  arrive 
within  48  hours  following  the  fire.  Reviewing  the  records  of  42  large 
fires  (including  two  explosions)  covering  a  21-year  period,  Russel 
concluded  that  there  was  not  one  instance  in  which  rain  followed 
within  48  hours  as  an  evident  consequence  of  the  fire.  He  further  cal- 
culated that  to  get  increased  rainfall  of  60  percent  over  a  land  surface 
of  52,000  square  feet  at  Sidney  would  require  9  million  tons  of  coal  per 
day,  in  an  effort  to  show  what  magnitude  of  energy  expenditure  was 
necessary  and  how  futile  such  an  attempt  would  be.23 

Toward  the  latter  part  of  the  19th  century  there  were  a  number  of 
ideas  and  devices  invented  for  producing  rain  artificially.  In  1880 
David  Ruggles  of  Virginia  patented  what  he  said  was  "a  new  and  use- 
ful mode  of  producing  rain  or  precipitating  rainfalls  from  rainclouds, 
for  the  purpose  of  sustaining  vegetation  and  for  sanitary  purposes." 
His  plan  included  a  scheme  by  which  balloons  carrying  explosives  were 
sent  up  into  the  air,  the  explosives  to  be  detonated  in  the  upper  air  "by 
electric  currents."  24 

19  Lanham,  I.  A..  "The  Great  Fires  of  1871  in  the  Northwest."  The  Journal  of  the  Frank- 
lin Institute,  vol.  64,  No.  1.  July  1872,  pp.  46-47. 

20  IMd.,  p.  47. 

21  Trowlirirtge,  John,  "Great  Fires  and  Rain-storms."  The  Popular  Science  Monthly,  vol.  2, 
December  1872.  p.  211. 

22  Tbid. 

23  Report  of  an  address  bv  H.  C.  Russel  was  given  in  Science,  vol.  3,  No.  55,  Feb.  22.  1884, 
pp.  229-230. 

24  "New  Method  of  Precipitating  Rain  Falls,"  Scientific  American,  vol.  43,  Aug.  14.  1S80, 
p.  106. 


G.  H.  Bell  suggested  a  rainmaking  device,  consisting  of  a  hollow 
tower  1.500  feet  high,  through  which  air  was  to  be  blown  into  the 
atmosphere,  the  volume  of  the  up-rushing  air  to  be  increased  through 
use  of  a  s}^stem  of  tubes  around  the  tower.  The  inventer  consider  that 
the  same  system  could  be  used  to  prevent  rain,  by  reversing  the  blower 
so  that  the  descending  air  might  "annihilate"  the  clouds.25 

Still  other  schemes  and  contrivances  were  proposed  and  patented. 
J.  B.  Atwater  was  granted  a  patent  in  1887  for  a  scheme  to  dissipate 
tornadoes  by  detonating  an  explosive  charge  in  their  centers,  and  an- 
other was  granted  to  Louis  Gathman  in  1891  for  seeding  clouds  for  rain 
by  exploding  a  shell  containing  "liquid  carbonic  acid  gas"  at  cloud 
height,20  the  latter  concept  antedating  by  over  50  years  the  more  recent 
carbon  dioxide  seeding  projects. 

There  continued  to  be  adherents  to  the  idea  that  explosions  could 
cause  rainfall.  This  belief  was  reinforced  by  "evidence"  of  such  a  con- 
nection in  a  book  by  Edward  Powers,  called  "War  and  the  Weather," 
published  in  1871  and  1890  editions,  in  which  the  author  recounted  the 
instances  in  which  rain  followed  battles,  mostly  from  North  America 
and  Europe  during  the  19th  century.27 

Powers  was  convinced  that : 

The  idea  that  rain  can  be  produced  by  human  agency,  though  sufficiently 
startling,  is  not  one  which,  in  this  age  of  progress,  ought  to  be  considered  as 
impossible  of  practical  realization.  Aside  from  its  connection  with  the  supersti- 
tions of  certain  savage  tribes,  it  is  an  opinion  of  comparatively  recent  origin,  and 
is  one  which  cannot  be  regarded  as  belonging,  in  any  degree,  to  a  certain  class  of 
notions  which  prevail  among  the  unthinking;  *  *  *  on  the  contrary,  it  is  one 
which  is  confined  principally  to  those  who  are  accustomed  to  draw  conclusions 
only  from  adequate  premises,  and  *  *  *  founded  on  facts  which  have  come  under 
their  own  observation.28 

In  tones  somewhat  reminding  us  of  those  urging  a  greater  Federal 
research  effort  in  recent  years,  Powers  proposed  that  experiments  be 
undertaken  for  economic  benefit : 

Judging  from  the  letters  which  I  have  received  since  commencing  in  1870  an 
attempt  to  bring  forward  the  subject  of  rains  produced  by  cannon  tiring.  I  believe 
that  the  country  would  regard  with  interest  some  experiments  in  the  matter,  and 
would  not  begrudge  the  expense,  even  if  they  should  prove  unsuccessful  in  leading 
to  a  practical  use  of  the  principle  under  discussion.  In  some  matters  connected 
wTith  science,  the  Government  has  justly  considered  that  an  expenditure  of  public 
funds  was  calculated  to  be  of  public  benefit:  but  where,  in  anything  of  tiie  kind 
it.  has  ever  undertaken,  has  there  been  so  promising  a  field  for  such  actions  as 

Powers,  upon  examining  the  records  of  many  battles,  said  : 

Let  us  proceed  to  facts — facts  not  one  of  which,  perhaps,  would  be  of  a  in- 
significance if  it  stood  alone  and  unsupported  by  the  others;  but  which,  taken 
in  the  aggregate,  furnish  the  strongest  evidence  that  heavy  artillery  firing 
has  an  influence  on  the  weather  and  tends  to  bring  rain. 11 

Perhaps  influenced  by  the  arguments  of  Powers  and  others,  in 
1890  the  U.S.  Congress  had  become  so  much  interested  in  and  gained 

Another  Ka in  Controller."  Scientific  American,  vol.  4:{.  Aug,  21.  1SSO.  p  11M. 

26  Harrington,  Mark  W..  "Weather-making,  Ancient  and  Modern,"  Smithsonian  Institu- 
tion Annual  Report,  to  July  1894,  pp.  249  1270. 

-'■  I'owers.  IMward.  "War  and  the  Weather."  Delavan.  Wis..  10.  Powers.  1890,  revised 
edition,  202  pp.  (An  earlier  edition  was  published  in  Chicago  in  1871.  Incidentally,  the 
plates  for  the  first  edition  were  deal  roved  in  the  Chicago  lire,  and  I'owers  did  not  have  an 
opportunity  to  complete  his  revision  until  1890. ) 

-*  Ihid..  p.  5. 

■  Ihid..  p.  143. 

*  Ihid.,  p.  11. 


such  faith  in  the  possibility  of  weather  modification  that  funds 
we  re  appropriated  to  support  experiments  to  be  carried  out  under 
the  auspices  of  the  Forestry  Division  of  the  U.S.  Department  of 
Agriculture.  The  initial  $2?0p0  appropriated  was  increased  first  to 
$7,000,  and  finally  to  $10,000.  in  the  first  federally  sponsored  weather 
modification  project.  Of  the  total  appropriated.  $9,000  was  to  be 
spent  on  held  experiments.  Gen.  Robert  St.  George  Dyrenforth  was 
selected  by  the  Department  of  Agriculture  to  direct  these  tests,  hav- 
ing earlier  conducted  tests  near  Utiea,  X.Y.,  and  Washington,  D.C.. 
using  balloons  and  rockets  carrying  explosives.  The  principal  ex- 
periments were  executed  near  Midland,  Tex.,  using  a  variety  of  ex- 
plosive devices,  detonated  singly  and  in  volleys,  both  on  the  ground 
and  in  the  air.31 

According  to  an  interesting  account  by  Samuel  Hopkins  Adam-. 
Dyrenforth  arrived  in  Texas  on  a  hot  day  in  August  1891  with  a 
company  of  80  workers,  including  "*  *  *  chemists,  weather  observers, 
balloon  operators,  electricians,  kitefiiers,  gunners,  minelayers,  sap- 
pers, engineers,  and  laborers  *  *  *  together  with  some  disinterested 
scientists,  who  were  to  serve  as  reporters."  32  Adams  discusses  the  ap- 
paratus which  Dyrenforth  took  with  him  : 

The  expedition's  equipment  was  impressive.  There  were  68  balloons  of  from  10 
to  12  feet  in  diameter,  and  one  of  20  feet — all  to  be  hlled  with  an  explosive  mixture 
of  hydrogen  and  oxygen.  There  were  also  sixty  6-inch  mortars,  made  of  pipe,  and 
several  tons  of  rackarock  (a  terrifying  blend  of  potassium  chlorate  and  nitro- 
benzol  that,  was  the  general's  favorite  "explodent"  >,  dynamite,  and  blasting 
powder.  Finally,  there  were  the  makings  of  a  hundred  kites,  to  be  assembled  on  the 
scene,  and  sent  up  with  sticks  of  dynamite  lashed  to  them.  The  congressional 
$9,000  fell  considerably  short  of  sufficing  for  so  elaborate  an  outfit,  but  expectant 
Texans  chipped  in  with  liberal  contributions  and  the  railroads  helped  out  by  sup- 
plying free  transportation.1" 

Dyrenforth  carried  out  five  series  of  trials  during  1891  and  1892  : 
one  period  of  sustained  cannonading  coincided  with  a  heavy  down- 
pour, and  the  apparent  connection  provided  support  to  the  credi- 
bility of  many  people,  who  accepted  the  hypotheses  as  confirmed. 
Dyrenforth  gave  optimistic  and  promising  reports  of  his  results: 
however,  meterologists  and  other  scientists  were  critical  of  his  work. 
It  does  not  appear  that  the  Forestry  Division  was  fervently  ad- 
vocating the  research  program  for  which  it  had  responsibility.  In 
1891,  Bernhard  E.  Fernow,  Chief  of  the  Division  of  Forestry,  re- 
ported to  the  Secretary  of  Agriculture  his  sentiments  regarding  the 
experiments  which  were  to  be  conducted  in  the  coming  summer,  with 
a  caution  reminiscent  of  the  concerns  of  many  meterologists  of  the 
1970°s : 

The  theories  in  regard  to  the  causes  of  storms,  and  especially  their  local  and 
temporal  distribution,  are  still  incomplete  and  unsatisfactory.  It  can  by  no  means 
be  claimed  that  we  know  all  the  causes,  much  less  their  precise  action  in  precipi- 
tation. It  would,  therefore,  be  presumptuous  to  deny  any  possible  effects  of  ex- 
plosions ;  but  so  far  as  we  now  understand  the  forces  and  methods  in  precipitating 
rain,  there  seems  to  be  no  reasonable  ground  for  the  expectation  that  they  will  be 
effective.  We  may  say,  then,  that  at  this  stage  of  meteorological  knowledge  we 
are  not  justified  in  expecting  any  results  from  trials  as  proposed  for  the  predtre- 
tion  of  artificial  rainfall,  and  that  it  were  better  to  increase  this  knowledge  first 

31  Fleagle.  "Background  and  Present  Status  of  Weather  Modification."  1968,  pp.  7-8. 

32  Adams.  Samuel  Hopkins.  The  New  Yorker.  Oct.  9,  1952,  pp.  93-100. 
*>  Ibid.,  i«.  !.'4. 


by  simple  laboratory  investigations  and  experiments  preliminary  to  experiment 
on  a  larger  scale.34 

In  1893,  the  Secretary  of  Agriculture  asked  for  no  more  public  funds 
for  support  of  this  project.35 

Fleagle  tells  about  the  use  of  36  "hail  cannons"  by  Albert  Stiger,  a 
town  burgomaster,  on  the  hills  surrounding  his  district  in  Austria  in 

Tbe  hail  cannon  consisted  of  a  vertically  pointing  three-centimeter  mortar 
above  which  was  suspended  the  smokestack  of  a  steam  locomotive.  This  device 
not  only  produced  an  appalling  sound,  but  also  created  a  smoke  ring  a  meter  or 
more  in  diameter  which  ascended  at  about  one  hundred  feet  per  second  and 
produced  a  singing  note  lasting  about  ten  seconds.  Initial  successes  were  impres- 
sive, and  the  hail  cannon  was  widely  and  rapidly  copied  throughout  central 
Europe.  Accidental  injuries  and  deaths  were  numerous,  and  in  1902  an  inter ua- 
tional  conference  was  called  by  the  Austrian  government  to  assess  the  effects  of 
the  hail  cannon.  The  conference  proposed  two  tests,  one  in  Austria  and  one  in 
Italy,  the  results  of  which  thoroughly  discredited  the  device.36 

Though  unsuccessful,  the  work  of  Dyrenforth  and  others  had  in- 
spired belief  in  the  possibilities  of  drought  alleviation  such  that  a 
number  of  unscrupulous  "rainmakers"  were  able  to  capitalize  on  the 
situation.  Halacy  gives  an  account  of  a  famous  rainmaker  of  the  early 
20th  century,  Charles  Warren  Hatfield,  who  operated  for  about  10 
years  in  the  western  United  States.  With  a  25-foot  platform  and  a 
secret  device  for  dispensing  chemicals,  he  claimed  to  create  rain  over 
extensive  areas.  In  1916.  Hatfield  contracted  with  the  city  of  San  Diego 
to  alleviate  drought  conditions  and  was  to  be  paid  $1,000  for  each  inch 
of  rain  produced.  When  20  inches  of  rain  coincidentally  fell  nearby, 
the  resulting  floods  destroyed  a  dam,  killed  17  people,  and  produced 
millions  of  dollars  damage.  Hatfield,  faced  with  a  choice  of  assuming 
financial  responsibility  for  the  lawsuits  or  leaving  the  city  without  pay, 
chose  the  latter.37 

One  of  Hatfield's  accomplices  was  a  colorful  racetrack  reporter  from 
Xew  York,  who  met  and  joined  Hatfield  in  California  in  1912,  named 
James  Stuart  Aloysius  MacDonald,  alias  Colonel  Stingo,  "the  Honest 
Rainmaker."  Over  his  half -century  career  as  a  writer,  mostly  for  var- 
ious horseracing  journals.  MacDonald  reportedly  involved  himself  in 
various  schemes  for  quick  profit,  including  weather  changing  projects 
on  both  the  west  and  east  coasts.  Contracts  with  clients  were  drawn  up 
with  terms  for  remuneration  that  resembled  very  much  the  language 
of  success  or  failure  at  the  racetrack.  By  his  own  admission,  Mac- 
Donald  based  his  odds  for  success  on  past  weather  data  for  a  given 
area,  which  he  obtained  from  records  of  the  U.S.  Weather  Bureau  or 
the  Xew  York  Public  Library.88  MacDonald,  or  Colonel  Stingo,  was 
the  inspiration  for  a  Broadway  play  called  "The  Rainmaker"  which 
opened  in  1954. 


Espy's  L839  proposal  for  an  experiment  on  the  production  of  con- 
vection currents  and  water  vapor  condensation  at  high  altitudes  was 

■A  Fernow,  Rernhard  E..  in  report  to  Jeremiah  McClain  Rusk.  Secretary  of  Agriculture, 
1891,  an  reported  in  Ward,  "Artificial  Rain  ;  a  Review  of  the  Subject  to  the  Close  of  1889." 
1882.  p.  492. 

•  livers.  "History  of  Weather  .Modification."  1 1*74.  p.  5. 
38  Fleajcle.  "Rackpronnd  and  Present  Status  of  Weather  Modification,"  1968,  p.  9. 
:t7  Halacy,  "The  Weather  Changers,"  1968,  pp.  68  69. 
38  Liebling,  A.  J.,  "Profiles,"  The  New  Yorker,  Sept.  20,  1902,  pp.  43-71. 


based  on  sound  physical  principles.  Since  knowledge  of  atmospheric 
processes  was  expanding  and  unfolding  rapidly  at  the  time,  Hartman 
reminds  us  that  the  limited  usefulness  of  Espy's  weather  modification 
concepts  should  not  be  ascribed  to  faulty  logic,  but  rather  to  the  primi- 
tive understanding  at  the  time  of  the  complex  processes  in  precipita- 
tion, many  of  which  are  still  not  understood  satisfactorily.39 

The  understanding  which  meteorologists  have  today  about  precipi- 
tation has  been  learned  slowly  and  sometimes  painfull}^,  and,  while 
many  of  the  discoveries  haA'e  resulted  from  20th  century  research, 
some  important  findings  of  the  latter  part  of  the  19th  century  are 
fundamental  to  these  processes.  Important  results  were  discovered  in 
1875  by  Coulier  in  France  on  foreign  contaminant  particles  in  the 
normal  atmosphere,  and  quantitative  measurements  of  the  concentra- 
tions of  these  particles  were  achieved  by  Aitken  in  1879.  These  events 
established  a  basis  for  explaining  the  fundamental  possibility  for 
occurrence  of  precipitation.  Earlier,  it  had  been  learned  that  high 
supersaturations  were  required  for  the  formation  of  water  droplets.40 
Aitken  was  the  first  to  imply  that  there  are  two  types  of  nuclei,  those 
with  an  affinity  for  water  vapor  (hygroscopic  particles)  and  nuclei 
that  require  some  degree  of  supersaturation  in  order  to  serve  as  con- 
densation centers.  The  Swedish  chemist-meteorologists  of  the  1920's 
developed  a  theory  of  condensation  on  hygroscopic  nuclei  and  showed 
the  importance  of  sea-salt  particles.  In  the  1930's  in  Germany  and  the 
United  Kingdom,  a  series  of  measurements  were  conducted  on  the 
numbers  and  sizes  of  condensation  nuclei  by  Landsberg,  Judge,  and 
Wright.  Data  from  measurements  near  Frankfurt,  augmented  sub- 
sequently by  results  from  other  parts  of  the  world,  have  been  adopted 
as  the  standard  of  reference  for  condensation  nuclei  worldwide.41 

At  the  beginning  of  the  1930's  important  aspects  of  cloud  phys' 
were  not  yet  understood.  In  particular,  the  importance  of  thp  ic,ri  phu 
to  precipitation  was  not  yet  clarified,  though,  ever  since  the  turn  of 
the  century  meteorologists  were  aware  that  water  droplets  were  abun- 
dantly present  in  clouds  whose  temperatures  were  well  below  the  freez- 
ing point.  Little  was  known  about  the  microphysics  of  nucleation  of  ice 
crystals  in  clouds ;  however,  it  had  been  noted  that  rains  fell  only  after 
visible  glaeiation  of  the  upper  parts  of  the  clouds.  Understanding 
of  these  processes  was  essential  before  scientific  seeding  of  clouds  for 
weather  modification  could  be  pursued  rationally.  In  1933  Tor  Berg-er- 
on  presented  and  promulgated  his  now  famous  theory  on  the  initiation 
of  precipitation  in  clouds  containing  a  mixture  of  liquid  and  ice. 
W.  Findeisen  expanded  on  Bergeron's  ideas  and  published  a  clearer 
statement  of  the  theory  in  1938 ;  consequently,  the  concept  is  generally 
known  as  the  Bergeron-Findeisen  theory.42  in  his  investigation  of  the 
formation  of  ice  crystals,  Findeisen  was  of  the  opinion  that  they  crys- 
talled directly  from  the  vapor  (that  is,  by  sublimation)  rather  than 
freezing  from  droplets.  He  also  conjectured  that  quartz  crystals  might 
be  the  nuclei  responsible  for  this  process  and  even  foresaw  that  the 
mechanism  might  be  initiated  artificially  by  introducing  suitable 

33  Hartman,  "Weather  Modification  and  Control,"  1966,  p.  13. 

40  Ibid. 

41  Bvers.  "History  of  Weather  Modification,"  1974,  p.  7. 

42  Ibid.,  p.  8. 

*»  Ibid.,  pp.  8-9. 

34-857—79  5 


Findeisen  stated  emphatically  that  rain  of  any  importance  must 
originate  in  the  form  of  snow  or  hail,  though  Bergeron  had  admitted 
the  occurrence  of  warm  rain  in  the  tropics.  Though  many  meteorolo- 
gists doubted  that  the  ice  crystal  process  was  an  absolute  requirement 
for  rain,  they  had  been  unable  to  collect  evidence  from  aircraft  obser- 
vations. In  Germany  aerological  evidence  was  obtained  on  the  growth 
of  rain  drops  by  the  collision-coalescence  process  in  "warm"  clouds, 
but  the  papers  on  this  work  were  published  in  1940,  and  World  War 
II  restricted  communication  of  the  results  to  meteorologists  world- 
wide. Meanwhile  in  the  United  States,  papers  were  published  on  the 
theory  of  the  warm  rain  process.  In  1938,  Houghton  showed  that  pre- 
cipitation could  be  started  by  either  the  Bergeron  process  or  by  the 
collision-coalescence  process.  He  noted  that  drops  could  be  formed  by 
condensation  on  "giant"  hygroscopic  nuclei  present  in  the  air  and  that 
growth  of  droplets  to  raindrop  size  was  possible  through  collision. 
G.  C  Simpson  elucidated  further  on  condensation  and  precipitation 
processes  in  1941,  disagreeing  with  Findeiseivs  rejection  of  "warm" 
rain  formation  by  the  collision-coalescence  process.44 


Starting  about  1920  and  continuing  for  about  two  decades  until 
the  outbreak  of  World  War  II,  there  were  a  number  of  experiments 
and  operations  intended  to  produce  rain  or  modify  the  weather  in 
some  other  way.  Although  some  of  these  activities  were  pusued  in  a 
scientific  manner,  others  were  less  so  and  were  directed  at  producing 
immediate  results;  all  of  these  projects  lacked  the  benefit  of  the  funda- 
mental knowledge  of  precipitation  processes  that  was  to  be  gained 
later  during  this  same  period,  the  discoveries  of  which  are  discussed 
in  the  preceding  subsection.  Various  schemes  during  this  period  in- 
cluded the  dispensing  of  materials  such  as  dust,  electrified  sand,  dry 
ice,  liquid  air,  and  various  chemicals,  and  even  the  old  idea  that  explo- 
sions can  bring  rain.  Field  tests  were  conducted  in  the  United  States, 
Germany,  the  Netherlands^  and  the  Soviet  Union. 

Byers  tells  .about  the  experimental  work  of  Dr.  E.  Leon  Chaffee, 
professor  of  physics  at  Harvard,  who  became  interested  in  the  possi- 
bility of  making  cloud  particles  coalesce  by  sprinkling  electrically 
charged  sand  over  the  clouds : 

Dr.  Chaffee  became  enthusiastic  about  the  idea  and  developed  in  his  laboratory 
a  nozzle  tor  charging  sand  and  dispersing  it  from  an  airplane.  The  nozzle  could 
deliver  sand  grains  having  surface  gradients  of  the  order  of  1.000  V/ein.  Flight 
experiments  were  carried  out  in  August  and  Seprcmber  of  1024  at  Aberdeen, 
Md..  with  an  airplane  scattering  the  sand  particles  in  the  clear  air  above  clouds 
having  tops  at  to  10,000  feet.  Dr.  Chaffee  reported  "success*'  in  the  reverse 
sense,  in  that  several  clouds  were  observed  to  dissipate  after  treatment.  The  tests 
were  well  publicized  in  newspapers  and  scientific  news  journals,  and  this  author, 
then  a  freshman  at  the  University  of  California,  recalls  that  his  physics  pro- 
fessors were  enthusiastic  about  the  idea.  Chaffee's  results  probably  would  not 
endure  the  type  of  statistical  scrutiny  to  which  experiments  of  this  kind  are 
subject  today.43 

Chaffee  considered  several  trials  successful,  since  clouds  were  dis- 
sipated after  being  sprayed  with  the  charged  sand.  It  has  been  pointed 

"  Ibid  .  p.  9. 
«  Ibid.,  p.  5. 


out,  however,  in  view  of  the  much  greater  experience  in  recent  years, 
that  scientists  must  be  extremely  cautious  in  ascribing  success  in  such 
experiments,  when  the  evidence  is  based  largely  on  visual  obser- 

In  the  Netherlands,  August  Veraart  successfully  produced  rain  by 
seeding  clouds  with  dry  ice  from  a  small  aircraft  in  1930.  This  was 
16  years  before  the  work  at  General  Electric  in  the  United  States,  when 
clouds  were  also  seeded  with  dry  ice,  initiating  the  modern  period  in 
the  history  of  weather  modification.  Since  Veraart  probably  did  not 
understand  the  mechanism  involved  in  the  precipitation  process  which 
he  triggered,  ho  did  not  realize  that  the  dry  ice  was  effective  in  develop- 
ment of  ice  crystals  by  cooling  supercooled  clouds,  and  his  success  was 
likely  only  a  coincidence.  Byers  observes  that  Veraart's  vague  con- 
cepts on  changing  the  thermal  structure  of  clouds,  modifying  tem- 
perature inversions,  and  creating  electrical  effects  were  not  accepted, 
however,  by  the  scientific  community.47  He  claimed  to  be  a  true  rain- 
maker and  made  wide,  sweeping  claims  of  his  successes.  He  died  in 
19o*2,  a  year  before  Bergeron's  theory  appeared,  not  aware  of  the  theo- 
retical basis  for  his  work.48 

Partly  successful  experiments  on  the  dissipation  of  fog  were  con- 
ducted by  the  Massachusetts  Institute  of  Technology  in  the  1930s, 
under  the  direction  of  Henry  G.  Houghton.  At  an  airfield  near  Round 
Hill,  Mass.,  fog  was  cleared  using  sprays  of  water-absorbing  solutions, 
particularly  calcium  chloride,  as  well  as  fine  particles  of  dry  hygro- 
scopic material.  Results  of  these  experiments,  which  predated  some  of 
the  present-day  foo-  dispersal  attempts  bv  some  30  vears,  were  reported 
in  1938. 19 

Weather  Modification  Sixce  1946 


The  following  chronology  of  "critical  events"  relating  to  weather 
modification  policy,  compiled  by  Fleagle.  unfolds  only  some  of  the 
major  events  and  activity  periods  which  have  occurred  since  the  his- 
toric discoveries  of  1946 : 50 

1946  :  Schaefer  demonstrated  seeding:  with  dry  ice. 

1947  :  Vonnegut  demonstrated  seeding  with  silver  iodide. 

1947-55 :  Irving  Langmuir  advertised  weather  modifieaton  widely  and  aggres- 

1947-  53:  General  Electric  field  experiments  ("Cirrus")  extended  evidence 
that  clouds  can  he  deliherately  modified,  but  failed  to  demonstrate  large  effects. 

1948-  50:  Weather  Bureau  Cloud  Physics  Project  on  cumulus  and  stratiform 
clouds  resulted  in  conservative  estimate  of  effects. 

1948-52 :  Commercial  operations  grew  to  cover  10  percent  of  United  States. 

1950:  Report  of  Panel  on  Meteorology  of  Defense  Department's  Research  and 
Development  Board  (Haurwitz,  Chairman)  was  adverse  to  Langmuir's  claims. 

1953:  Public  Law  83-256  established  President's  Advisory  Committee  on 
Weather  Control. 

45  McDonald.  James  E..  "An  Historical  Note  on  an  Early  Cloud-Modification  Experiment. 
Bulletin  of  the  American  Meteorological  Society,  vol.  42.  No.  3,  March  1961,  p.  19o. 

47  Byers.  "History  of  Weather  Modification."  1947.  p.  6. 

48  Hartman.  "Weather  Modification  and  Control."  1966.  p.  15.  ,      ,  „ 

»  Houghton.  Henrr  G..  and  W.  H.  Radford.  "On  the  Local  Dissipation  of  Natural  bog. 
Papers  in  Physical  Oceanography  and  Meteorology.  Massachusetts  Institute  of  Technology 
and  Woods  Hole  Oceanographic  Institution,  vol.  6,  No.  3.  Cambridge  and  Woods  Hole,  Mass., 
October  1938,  63  pp.  ,      „    -      ..     „  „  . 

50  Fleagle.  Robert  G  .  "An  Analysis  of  Federal  Policies  in  \\  eather  Modification.  Back- 
ground paper  prepared  for  use  by  the  U.S.  Department  of  Commerce  Weather  Modification 
Advisory  Board.  Seattle.  Wash.,  March  1977.  pp.  3-5. 


1953-54:  "Petterssen"  Advisory  Committee  organized  field  tests  on  storm  sys- 
tems, convective  clouds,  and  cold  and  warm  fog  (supported  by  the  Office  of 
Naval  Research,  the  Air  Force,  the  Army  Signal  Corps,  and  the  Weather 
Bureau).  These  statistically  controlled  experiments  yielded  results  which  have 
been  substantially  unchanged  in  subsequent  tests. 

1957:  Report  of  Advisory  Committee  (Orville,  Chairman)  concluded  that  tests 
showed  15  percent  increase  in  orographic  winter  precipitation. 

1957 :  Major  cut  in  research  support  across  the  board  by  Defense  Department 
sends  major  perturbation  through  research  structure. 

195S:  Public  Law  85-510  assigned  lead  agency  responsibility  to  the  National 
Science  Foundation  (NSF). 

1959:  Commercial  operations  had  diminished  to  cover  about  one  percent  of 
the  United  States. 

1961 :  First  hurricane  seeding  under  Project  Stormfury. 

1961 :  Bureau  of  Reclamation  authorized  by  Congress  to  conduct  research  in 
weather  modification. 

1961 :  RAND  report  on  weather  modification  emphasized  complexity  of  atmos- 
pheric processes  and  interrelation  of  modification  and  prediction. 

1962-70:  Randomized  field  experiments  established  magnitude  of  orographic 

1964:  Preliminary  report  of  National  Academy  of  Sciences/Committee  on 
Atmospheric  Sciences  (NAS/CAS)  roused  anger  of  private  operators  and  stimu- 
lated the  evaluation  of  operational  data. 

1964-present :  Department  of  the  Interior  pushed  the  case  for  operational  seed- 
ing to  augment  water  supplies. 

1966:  NAS/CAS  report  1S50  laid  the  basis  for  expanded  Federal  programs. 

1966 :  Report  of  NSF  Special  Commission  on  Weather  Modification  and  an  NSF 
symposium  called  attention  to  social,  economic,  and  legal  aspects. 

1966:  Interdepartmental  Committee  for  Atmospheric  Sciences  (ICAS)  report 
f  Newell,  Chairman)  proposed  expanded  Federal  support  to  $90  million  by  1970. 

1966-  68 :  Efforts  of  the  Departments  of  Commerce  and  Interior  to  gain  lead 
agency  status  were  unsuccessful. 

1967:  ICAS  recommended  that  Commerce  be  designated  as  lead  agency. 
1967:  S.  2916,  assigning  lead  agency  responsibility  to  the  Department  of  Com- 
merce :  passed  the  Senate  but  did  not  become  law. 

1967-  72  :  Military  operational  programs  conducted  in  Vietnam. 
1968:  Public  Law  90-407  removed  the  NSF  mandate  as  lead  agency. 
1968  :  Detrimental  effects  of  acid  rain  reported  from  Sweden. 

1969:  Public  Law  91-190  (National  Environmental  Policy  Act)  required  im- 
pact statements. 

1970;  Massachusetts  Institute  of  Technology  Study  of  Critical  Environmental 
Problems  called  attention  to  inadvertent  effects  on  climate. 

1970  :  Stratospheric  contamination  by  SST's  suggested. 

1971 :  Departments  of  Commerce  and  Interior  carried  out  operational  programs 
in  Oklahoma  and  Florida. 

1971  :  Public  Law  92-205  required  filing  of  reports  of  non-Federal  weather 
modification  activities  with  the  Department  of  Commerce. 

1971  :  International  Study  of  Man's  Impact  on  Climate  raised  this  issue  to  inter- 
national level. 

1971 :  NAS/CAS  report  on  priorities  for  the  1970's  emphasized  need  for  atten- 
tion to  management  and  policy  problems  of  weather  modification. 

1971:  Federal  Council  for  Science  and  Technology  approved  seven  national 
projects  under  various  lead  agencies. 

1971-72:  First  technological  assessments  of  weather  modification  projects  are 
favorable  to  operational  programs. 

1971-74  :  Climate  impact  assessment  program  ( CTAP)  of  Department  of  Trans- 
portation indicates  potentially  serious  consequences  of  large  SST  fleet  but  sug- 
gests ways  to  ameliorate  the  problem. 

1972:  Failure  of  Soviet  wheat  crop  and  drought  in  Sahel  emphasized  critical 
need  for  understanding  climate  and  the  value  of  effective  weather  modification. 

1973:  Weather  modification  budget  reduced  by  impoundment  from  $25.4  million 
to  $20.2  million. 

1973  :  Five  national  projects  deferred  or  terminated. 

1973:  NAS/CAS  report  on  weather  and  climate  modification  confirmed  earlier 
conclusions  and  recommended  lead  agency  status  for  NOAA. 


1974  :  Stratospheric  contamination  by  freon  reported. 

1974 :  Domestic  Council  organized  panels  in  climate  change  and  weather 

1974 :  General  Accounting  Office  report  on  weather  modification  criticized 
weather  modification  program  and  pointed  to  need  for  lead  agency. 

1974 :  Defense  Department  released  information  on  operations  in  Vietnam. 

1974 :  The  United  States  and  the  U.S.S.R.  agreed  to  a  joint  statement  intended 
"to  overcome  the  dangers  of  the  use  of  environmental  modification  techniques  for 
military  purposes." 

1975 :  World  Meteorological  Organization  Executive  Committee  proposed  cumu- 
lus experiment  perhaps  in  Africa  or  Iran. 

1975 :  Department  of  Transportation  CIAP  report  indicated  that  a  fleet  of  500 
SST's  would  deplete  ozone  significantly,  but  suggested  that  cleaner  engines  could 
be  developed. 

1976:  Chinese  disapproval  resulted  in  abandoning  plans  for  Stormfury  in  the 
western  Pacific. 

1976 :  Hearings  held  on  three  weather  modification  bills  by  Senate  Commerce 

1976:  The  National  Weather  Modification  Policy  Act  of  1976  (Public  Law  94- 
859)  enacted  requiring  study  of  weather  modification. 

1977 :  Exceptionally  dry  winter  in  the  west  stimulates  State  operational  pro- 
grams intended  to  increase  mountain  snowpack. 

Since  the  completion  of  Fleagle's  list  above  in  March  1977,  at  least 
three  other  activities  of  equivalent  significance  ought  to  be  noted : 

1977  :  The  U.S.  Department  of  Commerce  Weather  Modification  Advisory  Board 
established  in  April  1977  and  initiated  a  major  study  on  a  recommended  national 
policy  and  Federal  program  of  research  in  weather  modification,  in  accordance 
with  requirements  to  be  fulfilled  by  the  Secretary  of  Commerce  under  Public  Law 
94-490,  the  National  Weather  Modification  Policy  Act  of  1976. 

1977  :  The  United  Nations  General  Assembly  approved  a  treaty  banning  environ- 
mental modification  activities  for  hostile  purposes  on  May  18,  1977  ;  and  the  treaty 
opened  for  signature  by  the  member  nations. 

1978 :  The  Report  of  the  Commerce  Department's  Weather  Modification  Advi- 
sory Board  transmitted  through  the  Secretary  of  Commerce  to  the  Congress. 

The  history  of  the  modern  period  of  weather  modification  which 
follows  is  essentially  that  of  the  two  decades  following  the  monumental 
discoveries  of  1946.  An  excellent  account  of  the  history  of  weather 
modification,  which  emphasizes  this  period,  has  been  prepared  by 
Byers.51  This  work  has  been  very  helpful  in  some  of  the  material  to 
follow  and  is  referenced  frequently.  The  late  1960's  and  the  1970's  are 
so  recent  that  events  during  this  period  are  discussed  in  various  sections 
of  the  report  as  ongoing  activities  or  events  leading  to  current  activities 
in  weather  modification  research  programs,  operations,  and  policy 
decisions  rather  than  in  this  chapter  as  an  integral  part  of  an  updated 
history  of  the  subject. 


The  modern  era  of  scientific  weather  modification  begaai  in  1946, 
when  a  group  of  scientists  at  the  General  Electric  Co.  demonstrated 
that,  through  "seeding,"  a  cloud  of  supercooled  water  droplets  could 
be  transformed  into  ice  crystals  and  precipitation  could  be  induced. 
These  were  not  traditional  meteorologists,  though  their  leader.  Dr. 
Irving  Langmuir,  was  a  famous  physicist  and  Nobel  laureate.  He  and 
his  assistant,  Vincent  J.  Schaefer,  had  been  working  for  3  years  on 
cloud  physics  research,  however,  in  which  they  were  studying  particle 
sizes,  precipitation  static,  and  icing.  Their  field  research  was  carried  on 

Byers,  "History  of  Weather  Modification,"  1974,  pp.  3-44. 


at  the  summit  of  Mt.  Washington.,  X.H..  where  they  observed  super- 
cooled clouds  which  often  turned  into  snowstorms.52 

In  an  attempt  to  simulate  field  conditions.  Schaefer  contrived  a 
laboratory  setup  using  a  home  freezer  lined  with  black  velvet,  with  a 
light  mounted  so  as  to  illuminate  ice  crystals  that  might  happen  to 
form  in  the  box.  Breathing  into  the  box,  whose  temperature  was  about 
—  23°  C,  produced  fog  but  no  ice  crystals,  even  when  various  sub- 
stances— including  sand,  volcanic  dust,  sulfur,  graphite,  talc,  and 
salt — were  dropped  in  as  possible  sublimation  nuclei.53  On  July  12. 
19-16,  Schaefer  wanted  to  lower  the  freezer  temperature  somewhat,  so 
he  inserted  a  large  piece  of  dry  ice.  and.  in  an  instant,  the  air  was 
full  of  millions  of  ice  crystals.  He  discovered  that  even  the  tiniest 
piece  of  dry  ice  produced  the  same  etfect.  In  fact,  dry  ice  had  no 
direct  effect  on  the  supercooled  cloud;  producing  an  air  temperature 
below  -  39°  C  was  critical.54 

In  his  paper  on  the  laboratory  experiments,  published  in  the  No- 
vember 15, 1946.  issues  of^Sciencev  Schaefer  stated  : 

It  is  planned  to  attempt  in  the  near  future  a  large-scale  conversion  of  super- 
cooled clouds  in  the  atmosphere  to  ice  crystal  clouds,  by  scattering  small  frag- 
ments of  dry  ice  into  the  cloud  from  a  plane.  It  is  believed  that  such  an  opera- 
tion is  practical  and  economically  feasible  and  that  extensive  cloud  systems  can 
be  modified  in  this  way.53 

Two  days  before  the  paper  appeared,  on  Xovember  13,  1946, 
Schaefer  made  his  historic  flight,  accomplishing  man's  first  scientific 
seeding  of  a  supercooled  cloud,  as  he  scattered  three  pounds  of  dry  ice 
along  a  3-mile  line  over  a  cloud  to  the  east  of  Schenectady,  X.Y.  At 
14.000  feet  the  cloud  temperature  was  —20°  C.  and  in  about  §  minutes 
after  seeding  the  entire  cloud  turned  into  snow,  which  fell  2,000  feet 
before  evaporating.56 

Dr.  Bernard  Vonnegut  had  also  worked  on  aircraft  icing  research 
and  in  1946  at  General  Electric  was  pursuing  a  variety  of  nueleation 
problems ;  but.  after  Schaefer's  laboratory  experiments,  he  again 
turned  his  attention  to  ice  nueleation  research.  He  discovered  that 
silver  iodide  and  lead  iodide  had  crystal  structures  close  to  that  of  ice 
and  were  also  insoluble  in  water,  and  after  repeated  initial  failures, 
owing  to  impurities  in  the  material,  Vonnegut  was  able  to  produce  ice 
crystals,  using  very  pure  silver  iodide  powder,  at  temperatures  only  a 
few  degrees  below  freezing.  Soon  means  were  developed  for  generating 
silver  iodide  smokes,  and  man's  first  successful  attempt  at  artificial 
nueleation  of  supercooled  clouds  was  accomplished.57 

Langmuir  explained  that  dry  ice  could  make  ice  crystals  form  by 
lowering  the  temperature  to  that  required  for  natural  nueleation  on 
whatever  might  be  present  as  nuclei,  or  even  in  the  absence  of  all 
nuclei;  however,  the  silver  iodide  provided  a  nucleus  that  was  much 
more  efficient  than  those  occurring  naturally.58 

"  Ibid.,  pp.  9-10. 

"  Halacy,  "The  Weather  Changers/'  ions.  pp.  S2-S3. 

«  langmuir.  Irvinp.  "The  Growth  of  Particles  in  Smoke,  and  Clouds  and  the  Production 
of  Snow  from  Supercooled  Clouds. Proceedings  of  the  American  Philosophical  Society,  vol. 
92,  no.  3,  July  1048,  p.  182.  '  ,  ,  _  , 

Schaefer,  Vincent  J..  "The  Production  of  Ice  Crystals  in  a  Cloud  of  Supercooled  Water 
Droplets.'-  Science,  vol.  U>4.  No.  2707.  Nov.  15.  1946,  p.  459. 

"  Byers,  "History  of  Weather  Modification,"  1074.  p.  12. 

57  H>id  .  p.  13. 

M  Langmuir,  Irvine.  "Cloud  Seeding  by  Menus  of  Dry  Ice.  Silver  Iodide,  and  Sodium 
Chloride."  Transactions  of  the  New  York  Academy  of  Sciences,  ser.  II,  vol.  14.  November 
1951,  p.  40. 


Following  Schaefer's  successful  flight  of  November  13,  1946,  and  in 
the  months  and  immediate  years  thereafter,  Langmuir  was  quoted  in 
the  popular  press  as  being  very  optimistic  in  his  predicted  benefits 
from  weather  modification.  In  a  1948  paper  he  said  that  k>*  *  *  it 
becomes  apparent  that  important  changes  in  the  whole  weather  map 
can  be  brought  about  by  events  which  are  not  at  present  being  con- 
sidered by  meteorologists."  59  His  publications  and  informal  statements 
of  this  character  touched  off  years  of  arguments  with  professional 
meteorologists,  by  whom  refutation  was  difficult  in  view  of  Langmuir s 
standing  in  the  scientific  community.  His  enthusiasm  for  discussing 
the  potential  extreme  effects  from  weather  control  was  unrestrained 
until  his  death  in  1957. 60 


Project  Cirrus 

Although  the  business  of  the  General  Electric  Co.  had  not  been  in 
meteorology,  it  supported  the  early  research  of  Langmuir  and  his 
associates  because  of  the  obvious  importance  of  their  discoveries. 
Realizing  that  weather  modification  research  was  more  properly  a  con- 
cern of  the  Federal  Government,  the  company  welcomed  the  interest 
of,  and  contract  support  from,  the  U.S.  Army  Signal  Corps  in 
February  1947.  Subsequently,  contract  support  was  augmented  by  the 
Office  of  Naval  Research,  the  U.S.  Air  Force  provided  flight  support, 
and  the  U.S.  Weather  Bureau  participated  in  a  consultative  role.  The 
entire  program  which  followed,  through  1951,  under  this  arrangement, 
including  the  field  activities  by  Government  agencies  and  the  labora- 
tory work  and  general  guidance  by  General  Electric,  was  designated 
''Project  Cirrus."  61  According  to  Byers : 

The  most  pronounced  effect  produced  by  Project  Cirrus  and  subsequently  sub- 
stantiated by  a  number  of  tests  by  others,  was  the  clearing  of  paths  through 
supercooled  stratus  cloud  layers  by  means  of  seeding  from  an  airplane  with  dry 
ice  or  with  silver  iodide.  When  such  clouds  were  not  too  thick,  the  snow  that  was 
artificially  nucleated  swept  all  the  visible  particles  out  of  the  cloud.  *  *  *  In  one 
of  the  first  flights,  *  *  *  the  supercooled  particles  in  stratus  clouds  were  removed 
using  only  12  pounds  of  dry  ice  distributed  along  a  14-mile  line.  In  later  flights 
even  more  spectacular  results  were  achieved,  documented  by  good  photography. BL' 

Initial  Project  Cirrus  studies  were  made  during  the  summer  of 
1947  on  cumulus  clouds  near  Schenectady,  but  the  important  seeding 
experiments  were  conducted  the  following  year  in  New  Mexico.  Also 
during  1947,  there  was  an  attempt  on  October  13  to  modify  a  hurricane 
east  of  Jacksonville,  Fla.,  through  seeding  with  dry  ice.63  Visual  ob- 
servations, reported  by  flight  personnel,  seemed  to  indicate  a  pro- 
nounced change  in  the  cloud  deck  after  seeding,  and,  shortly  there- 
after, the  hurricane  changed  its  course  and  headed  directly  westward, 
striking  the  coasts  of  Georgia  and  South  Carolina.  Even  though  there 
was  precedent  for  such  erratic  behavior  of  hurricanes,  there  was 
speculation  about  the  effect  of  seeding  on  the  storm  path,  and  the  pos- 
sibility of  legal  responsibility  for  damages  which  might  be  caused  by 

59Lanfrmuir.  Irvinp.  "The  Production  of  Rain  by  a  Chain  Reaction  in  Cumulus  Clouds  at 
Temperatures  Above  Freezing."  Journal  of  Meteorology,  vol.  5.  No.  5.  October  1948.  p.  192. 
6°T?vprs.  "Historv  of  Weather  Modification."  1974.  pp.  13-14. 

61  ThH..  p.  14. 

62  Thirl. 

M  See  discussion  of  Project  Stormfury  in  ch.  5.  p.  290  ff. 


such  experiments  in  the  future  provided  reason  to  avoid  seeding 
thereafter  any  storms  with  the  potential  of  reaching  land.  The  legal 
counsel  of  the  General  Electric  Co.  admonished  Langmuir  not  to 
relate  the  course  of  the  hurricane  to  the  seeding;  however,  throughout 
the  remainder  of  his  career  he  spoke  of  the  great  benefit  to  mankind  of 
weather  control  and  of  the  potential  ability  to  abolish  evil  effects  of 
hurricanes.  As  a  result,  it  was  expected  that  the  U.S.  Weather  Bu- 
reau would  undertake  massive  efforts  in  weather  control.  Meteorolo- 
gists within  and  without  of  the  Bureau  were  in  a  defensive  position, 
with  many  other  scientists,  impressed  by  Langmuirs  arguments,  op- 
posing their  position.  Thus  great  controversies  which  developed 
between  Langmuir  and  the  Weather  Bureau  and  much  of  the  meteoro- 
logical community  followed  these  and  other  claims,  and  often 
resulted  from  the  fact  that  Langmuir  did  not  seem  to  fully  comprehend 
the  magnitude  and  the  mechanisms  of  atmospheric  phenomena.04 

Langmuir  wanted  to  ^work  where  he  thought  storms  originated 
rather  than  in  upstate  New  York.  He  chose  Xew  Mexico  as  operations 
area  for  Project  Cirrus,  also  taking  advantage  of  the  opportunity  to 
collaborate  there  with  Dr.  E.  J.  Workman  at  the  New  Mexico  Institute 
of  Mining  and  Technology,  whose  thunderstorm  research  included 
radar  observations  and  laboratory  experiments  on  the  effects  of  ire 
on  storm  electrification.  After  cloud-seeding  flights  there  in  October 
1948,  Langmuir  reported  that,  as  a  result  of  the  seeding,  rainfall  had 
been  produced  over  an  area  greater  than  40,000  square  miles  (about 
one-fourth  the  area  of  the  State  of  New  Mexico) . 63 

The  Project  Cirrus  group  returned  to  Xew  Mexico  in  July  1040, 
and  10  additional  seeding  nights  were  conducted.  When  Langmuir 
learned  that  Vonnegut  was  dispensing  silver  iodide  from  a  ground 
generator  in  the  same  area  and  had,  in  fact,  also  been  doing  so  during 
the  flights  of  the  previous  October,  he  concluded  that  both  the  July 
1919  results  and  the  widespread  effects  of  October  1948  were  caused 
by  the  silver  iodide  rather  than  the  dry  ice  seeding  as  he  had  theorized 
previously.  Spectacular  results  continued  to  be  reported  by  him. 
spurred  on  by  meteorologists'  challenges  to  his  statistical  methods 
and  conclusions.  Noting  that  Vonnegut  had  operated  the  ground 
generator  only  on  certain  days,  Langmuir  observed  that  rainfall 
responses  corresponded  to  generator  "on"  times,  leading  him  to  his 
controversial  "periodic  seeding  experiment.''  to  which  the  remainder 
of  his  life  was  devoted.66 

In  the  periodic  seeding  experiment,  the  silver  iodide  generators  were 
operated  in  an  attempt  to  effect  a  7-day  periodicity  in  the  behavior  of 
various  weather  properties.  Langmuir  was  convinced  that  unusual 
weekly  weather  periodicities  in  early  1950  resulted  from  periodic  seed- 
ings  begun  in  Xew  Mexico  in  December  1949.  concluding  that  the  effects 
were  more  widespread  than  he  felt  earlier  and  that  temperatures  and 
pressures  thousands  of  miles  away  were  also  affected.  Meteorologists 
observed  that,  while  these  correlations  were  the  most  striking  seen,  yet 
such  periodicities  were  not  uncommon.67  The  Weather  Bureau  under- 
took a  study  of  records  from  1919  to  1951  to  see  if  such  weather  perio- 

"  Ibid.,  pp.  14-16. 
■  Ibid.,  p.  1«. 
w  Ibid.,  p  in. 
r~  Ibid.,  pp.  in  20. 


dickies  had  occurred  in  the  past.  Glenn  W.  Brier,  author  of  the  report 
on  this  study,  indicated  that  a  T-day  component  in  the  harmonic  anal- 
ysis of  the  data  appeared  frequently,  though  seldom  as  marked  as  dur- 
ing the  periodic  seeding  experiment.68  Byers'  opinion  is  that  the  evi- 
dence appeared  just  as  reliable  for  occurrence  of  a  natural  periodicity 
as  for  one  controlled  artificially.  He  contends  that  the  most  important 
discoveries  in  cloud  physics  and  weather  modification  were  made  in  the 
General  Electric  Research  Laboratory  before  Project  Cirrus  was  orga- 
nized, that  the  effect  of  clearing  stratus  decks  was  shown  soon  after  the 
project  was  underway,  and  that  the  seeding  experiments  thereafter 
became  more  of  a  "program  of  advocacy  than  of  objective  proof."  The 
project  *  *  failed  to  demonstrate  that  seeding  of  cumulus  clouds 
increased  rainfall,  that  seeding  initiates  self -propagating  storms,  that 
the  atmosphere  responds  periodically  to  periodic  seeding,  or  that  a 
hurricane  could  be  deflected  in  its  path  by  seeding."  69 

Seeding  under  Project  Cirrus  ended  in  1951  and  the  final  report 
appeared  in  1953.  After  the  close  of  the  project,  Langmuir  continued 
his  analyses  and  wrote  two  more  papers  before  his  death  in  1957.  The 
final  paper  was  titled  "Freedom — the  Opportunity  To  Profit  From  the 
Unexpected."  a  report  that  Byers  feels  provided  a  fitting  philosophical 
close  to  his  career.70  The  Defense  Department  sponsored  another  series 
of  experiments,  called  the  Artificial  Cloud  Xucleation  Project,  from 
1051  to  1953. 

Tlie  Weather  Bureau  Cloud  Physics  project 

Amid  increasing  publicity  and  spectacular  claims  of  results  from 
cloud  seeding  in  Project  Cirrus,  the  U.S.  Weather  Bureau  initiated  in 
1048  a  project  to  test  cloud  seeding,  with  the  cooperation  of  the  Na- 
tional Advisory  Committee  for  Aeronautics,  the  Navy,  and  the  Air 
Force.  The  Cloud  Phvsics  Project,  the  first  systematic  series  of  seeding 
experiments  in  stratiform  and  cumuliform  clouds,  continued  for  2 
years,  with  flight  operations  in  Ohio,  California,  and  the  Gulf  States. 
Findings  of  Project  Cirrus  were  substantiated  in  that  striking  visual 
cloud  modifications  occurred:  however,  there  was  no  evidence  to  show 
spectacular  precipitation  effects,  and  the  experiments  led  to  a  conserva- 
tive assessment  of  the  economic  importance  of  seeding.71  Cloud  dissi- 
pation rather  than  new  cloud  development  seemed  to  be  the  general 
result  from  seeding,  the  only  precipitation  extractable  from  clouds  was 
that  contained  in  the  clouds  themselves,  and  cloud  seeding  methods  did 
not  seem  to  be  promising  for  the  relief  of  drought.72 

Bosults  of  the  cloud  physics  experiment  had  almost  no  effect  on 
the  prevalent  enthusiasm  at  the  time  for  rainmaking  through  cloud 
soedino-,  oxcent  in  the  "hard  core"  of  the  meteorology  community.73 
As  r  result  of  thes<*  experiments  and  the  interpretation  of  the  results, 
the  TToather  Bureau  and  its  successor  organizations  in  the  Commerce 
Department,  the  Environmental  Science  Services  Administration  and 
the  "National  Oceanic  and  Atmospheric  Administration,  have  been 

os  Brier.  Glenn  W..  "Seven-Dar  Periodicities  in  May  19.~2."  Bulletin  of  the  American 
Me^eorolosricPl  Societr.  vol.  35.  No.  3.  March  1954.  pp.  118-121. 
p?  B^ers.  "History  of  Weather  Modification."  1974.  pp.  20-21. 
70  Ibid.,  p.  20.. 

"  Flpfisrle.  Robert  G..  "Background  and  Present  Status  of  Weather  Modification."  196S. 
pp  0-10. 

■2  B-ers.  "^'storv  of  Weather  Modification."  1074.  pp.  10-17. 
»»  Ibid,,  p.  17. 


regarded  by  some  critics  as  unimaginative  and  overconservative  on 
weather  modification.74 

The  U.S.  experiments  of  1953-54 

In  1951  the  Weather  Bureau,  the  Army,  the  Navy,  and  the  Air  Force 
appointed  an  advisory  group,  chaired  by  Dr.  Sverre  Petterssen  of 
the  University  of  Chicago,  under  whose  advice  and  guidance  the 
following  six  weather  modification  projects  were  initiated : 75 

1.  Seeding  of  extratropical  cyclones,  sponsored  by  the  Office  of 
Naval  Research  and  conducted  by  Xew  York  University. 

2.  Seeding  of  migratory  cloud  systems  associated  with  fronts  and 
cyclones,  conducted  by  the  Weather  Bureau. 

3.  Treatment  of  connective  clouds,  supported  by  the  Air  Force  and 
conducted  by  the  University  of  Chicago. 

4.  Research  on  the~dissipation  of  cold  stratus  and  fog,  conducted 
by  the  Army  Signal  Corps. 

5.  Studies  of  the  physics  of  ice  fogs,  sponsored  by  the  Air  Force 
and  conducted  by  the  Stanford  Research  Institute. 

6.  Investigation  of  a  special  warm  stratus  and  fog  treatment  svs- 
tem,  sponsored  by  the  Army  and  conducted  by  Arthur  D.  Little,  Inc. 

Field  experiments  on  these  projects  were  carried  out  in  1953  and 
1954,  and  reports  were  published  under  the  auspices  of  the  American 
Meteorological  Society  in  195T.76 

The  purpose  of  the  extratropical  cyclone  seeding  project,  called 
Project  Scud,  was  to  "*  *  *  ascertain  whether  or  not  it  would  be 
possible  to  modify  the  development  and  behavior  of  extratropical 
cyclones  by  artificial  nucleation.  *  *  *"  77  Analysis  obtained  in  Scud 
from  Florida  to  Long  Island  showed  that  "*  *  *  the  seeding  in  this 
experiment  failed  to  produce  any  effects  which  were  large  enough  to  be 
detected  against  the  background  of  natural  meteorological  variance."  7S 

The  Weather  Bureau  project  on  migratory  cloud  systems  was  con- 
ducted in  western  Washington  on  cloud  systems  that  enter  the  area 
from  the  Pacific  during  the  rainy  winter  months.  This  project  was 
criticized  by  commercial  seeders  since  it  was  conducted  in  the  West, 
which  was  considered  "their  territory,"  and  by  those  who  accused  the 
Weather  Bureau  of  seeking  a  negative  result  to  support  their  conserva- 
tive view  toward  weather  modification.  Byers  feels  that  there  was  an 
attempt  to  avoid  this  negative  impression  by  giving  a  more  positive 
interpretation  to  the  results  than  the  data  possibly  justified.79  In  sum- 
marizing results.  Hall  stated: 

Considering  the  results  as  a  whole  there  is  no  strong  evidence  to  support  a  con- 
clusion that  the  seeding  produced  measurable  changes  in  rainfall.  *  *  *  the  eval- 
uations do  not  necessarily  furnish  information  on  what  the  effect  might  have  been 
with  more  or  less  intense  seeding  activity,  rate  of  release  of  dry  ice,  etc.  Also  it 

71  Pleagle.  "Background  and  Present  Status  of  Weather  Modification.''  1998,  p  10» 

«  Byers,  "History  of  Weather  Modification,"  1074.  p.  25. 

7.)  Prtterssen,  Sverre.  Jerome  Sp;ir.  Ferguson  Hall.  Roscoe  R.  Braham.  Jr.,  Louis  J.  Rat- 
tan. Horace  R.  Byers,  H.  J.  aufm  Kamoe.  J.  J.  Kelly,  and  H.  K.  Welcfcraann.  "Cloud  and 
Weather  Modification;  a  Croup  of  Field  Experiments."  Meteorological  Monographs,  vol.  2. 
No  11    American  Meteorological  Society,  Boston.  10."»7.  Ill  pp. 

"Petterssen,  Sverre.  "Reports  on  Experiments  with  Artificial  Cloud  Nucleation:  Intro- 
ductory Note."  In  Petterssen  et  al  .  "Cloud  and  Weather  Modification  :  ii  Croup  of  Field 

Experiments,"  Meteorological  Monographs,  vol.  2.  No.  n.  American  Meteoroio.^icnl  Society. 
Boston.  1957,  p,  S. 

T"  Spar.  Jerome  "Prolecl  Send."  in  Petterssen  et  al..  "Cloud  mid  Weather  Modification  ; 
:i  Group  of  Field  Experiments."  Meteorological  Monojrra plis.  vol.  2.  No.  11.  American  Mete- 
orological Society,  P.oston.  ior>7,  n  22. 

"Byers.  "History  of  Weather  Modification,"  1074.  p.  26. 


might  be  speculated  that  the  seeding  increased  rainfall  on  some  occasions  and 
decreased  it  on  others.80 

The  aim  of  the  University  of  Chicago  Cloud  Physics  project  was  as 
follows : 81 

The  formulation  of  a  consistent  and  immediately  applicable  picture  of  the 
processes  of  formation  of  cumulus  clouds,  charged  centers,  and  precipitation  with 
a  view  toward  testing  the  possibility  that  one  can  modify  these  processes  and 
influence  the  natural  behavior  of  clouds. 

So  that  as  many  cumulus  clouds  as  possible  could  be  tested,  work  was 
conducted  in  the  Middle  West  in  the  summer  and  in  the  Caribbean  in 
the  winter,  realizing  that  the  warm  trade-wind  cumulus  clouds  in  the 
latter  region  might  be  amenable  to  seeding  with  large  hygroscopic 
nuclei  or  water  spray,  and  that  the  ice-crystal  process  would  operate  to 
initiate  precipitation  in  the  colder  clouds  of  the  Middle  West.82,  Of  the 
numerous  conclusions  from  this  project 83  a  few  will  serve  to  indicate 
the  value  of  the  project  to  the  understanding  of  cloud  phenomena  and 
weather  modification.  In  the  Caribbean  tests,  water  spray  from  an  air- 
craft was  seen  to  increase  rainfall  as  determined  by  radar  echoes ;  anal- 
ysis showed  that  the  treatment  doubled  the  probability  of  occurrence  of 
a  radar  echo  in  a  cloud.  From  tests  on  dry  ice  seeding  in  the  Middle 
West  it  was  found  that  in  the  majority  of  cases  treated  clouds  showed 
an  echo,  while  untreated  ones  did  not,  although  the  sample  was  consid- 
ered too  small  to  be  significant.  In  all  cases  clouds  were  considered  in 
pairs,  one  treated  by  seeding  and  the  other  untreated,  and  only  those 
clouds  showing  no  echo  initially  were  chosen  for  study.84 

The  seeding  experiments  with  supercooled  stratus  clouds  by  the 
Army  Signal  Corps  essentially  substantiated  the  results  of  Project 
Cirrus;  however,  from  these  carefully  conducted  tests  a  number  of 
new  relationships  w^ere  observed  with  regard  to  seeding  rates,  spread 
of  glaciating  effect,  cloud  thickness,  overseeding,  and  cloud  formation 
after  seeding.S5  The  report  on  this  project  carefully  summarized  these 
relationships  and  conclusions  for  both  dry  ice  and  silver  iodide 

The  Air  Force  project  on  the  physics  of  ice  fogs,  conducted  by 
Stanford  Research  Institute,  was  intended  to  learn  the  relationship 
to  such  fogs  of  synoptic  situations,  local  sources  of  water,  and  pollu- 
tion. Investigations  in  Alaska  at  air  bases  showed  that  most  fogs 
developed  from  local  sources  of  water  and  pollution.  In  the  Arthur  L). 
Little  investigation  for  the  Army  attempts  were  made  to  construct 
generators  which  were  capable  of  producing  space  charges,  associated 
with  aerosols,  that  could  bring  about  precipitation  of  the  water  drop- 
lets in  warm  fogs  and  stratus.87 

»  Hail,  Ferguson.  "The  Weather  Bureau  ACN  Project."  In  Petterssen  et  al.,  "Cloud  and 
Weather  Modification  ;  a  Group  of  Field  Experiments,"  Meteorological  Monographs,  vol.  2. 
No.  11.  American  Meteorological  Society.  Boston.  1957.  pp.  45-46. 

slBraham.  Roscoe  R.,  Jr..  Louis  J.  Battan.  and  Horace  R.  Byers.  "Artificial  Nucleation 
of  Cumulus  Clouds."  In  Petterssen  et  al..  "Cloud  and  Weather  Modification  :  a  Group  of 
Field  Experiments,"  1957,  p.  47. 

&  Byers,  "History  of  Weather  Modification,"  1974,  pp.  26-27. 

83  Conclusions  are  precisely  spelled  out  in  somewhat  technical  terms  in  :  Braham,  Battan. 
and  Byers.  "Artificial  Nucleation  of  Cumulus  Clouds,"  1957,  pp.  S2-S3. 
fi  Byers,  "History  of  Weather  Modification,"  1974,  p.  27. 

86  IMd.  .    »  , 

86aufm  Kampe,  H.  J.,  J.  J.  Kelly,  and  H.  K.  Weickmann,  "Seeding  Experiments  m  Sub- 
cooled  Stratus  Clouds."  In  Petterssen  et  al..  "Cloud  and  Weather  Modification  :  a  Group  of 
Field  Experiments."  Meteorological  Monographs,  vol.  2,  No.  11.  American  Meteorological 
Society.  Boston,  1957,  p.  93.  ,        T  .     ,  . 

57  Petterssen,  "Reports  on  Experiments  With  Artificial  Cloud  Nucleation:  Introductory 
Note,"  1957,  p.  4. 


Brers,  in  retrospect,  wonders  why  the  results  of  this  series  of  six 
experiments,  which  were  carefully  controlled  statistically,  did  not 
receive  more  attention  than  was  accorded  them.  He  attributes  some 
of  this  lack  of  visibility  to  the  publication  in  the  somewhat  obscure 
monograph  of  the  American  Meteorological  Society  88  and  to  the  delay 
in  publishing  the  results,  since  the  Petterssen  committee  held  the  manu- 
scripts until  all  were  completed,  so  that  they  could  be  submitted  for 
publication  together.89 

Arizona  mountain  cumulus  experiments 

After  1954,  the  University  of  Chicago  group  joined  with  the  Insti- 
tute of  Atmospheric  Physics  at  the  University  of  Arizona  in  seeding 
tests  in  the  Santa  Catalina  Mountains  in  southern  Arizona.  These 
experiments  were  conducted  in  two  phases,  from  1957  through  1960 
and  from  1901  through  1964,  seeding  mostly  summer  cumulus  clouds, 
but  some  winter  storms,  with  silver  iodide  from  aircraft.  In  the  first 
phase,  analysis  of  precipitation  data  from  the  first  2  years  revealed 
more  rainfall  during  seeded  than  on  nonseeded  days ;  however,  during 
the  latter  2  years,  considerably  more  rainfall  was  achieved  on  non- 
seeded  days.  Combining  all  data  for  the  4  years  of  the  first  phase 
yielded  overall  results  with  more  rain  on  unseeded  days  than  on  seeded 
days;  hence,  the  experiments  were  modified  and  the  second  phase 
undertaken.  Of  the  3  years  in  the  second  phase,  only  one  showed  more 
rain  on  seeded  days  than  on  nonseeded  ones.  None  of  the  analyses 
attempted  could  support  the  hypothesis  that  airborne  silver  iodide 
seeding  increased  precipitation  or  influenced  its  area!  extent.  Byers 
suggests  that  the  failure  to  increase  rainfall  may  have  been  due  to  the 
fact  that  precipitation  initiation  resulted  from  the  coalescence  process 
rather  than  the  ice-crystal  process.90 

Project  Whitetop 

According  to  Byers,  perhaps  the  most  extensive  and  most  sophisti- 
cated weather  modification  experiment  (at  least  up  to  the  time  of 
Byers'  historical  review  in  1973)  was  a  5-year  program  of  summer 
convective  cloud  seeding  in  south-central  Missouri,  called  Project 
Whitetop.  Conducted  from  19G0  through  1964  by  a  group  from  the 
University  of  Chicago,  led  by  Dr.  Roscoe  11.  Braham,  the  purpose  of 
Whitetop  was  to  settle  with  finality  the  question  of  whether  or  not 
summer  convective  clouds  of  the  Midwest  could  be  seeded  with  silver 
iodide  to  enhance  or  initiate  precipitation.  Experimental  days  were 
divided  into  seeding  and  no  seeding  days,  chosen  randomly  from 
operational  days  suitable  for  seeding,  based  on  certain  moisture  cri- 
teria. Another  feature  of  the  project  was  the  attempt  to  determine  the 
extent  of  spreading  of  silver  iodide  smoke  plumes  from  the  seeding 
line.  Precipitation  effects  were  evaluated  by  radar  and  by  a  rain-gage 

Final  analysis  of  all  of  the  Project  Whitetop  data  showed  that  the 
overall  effect  was  that,  in  the  presence  of  silver  iodide  nuclei,  the  rain- 
fall was  less  than  in  the  unseeded  areas.  Byers  attributes  these  negative 

88  Petterssen  et  al..  "Cloud  and  Weather  Modification;  a  Group  of  Field  Experiments," 

*>  livers.  "History  of  Weather  Modification,"  11)74,  p.  2S. 

»°  Il)ld.,  p.  29. 

«  Ibid.,  pp.  20-30. 


results  to  the  physical  data  obtained  from  cloud-physics  aircraft.  "Most 
of  the  Missouri  clouds  produced  raindrops  by  the  coalescence  process 
below  the  freezing  line,  and  these  drops  were  carried  in  the  updrafts 
and  frozen  as  ice  pellets  at  surprisingly  high  subf reezing  temperatures 
(  —  5°  C  to  —10°  C)."  He  further  points  out  that  the  measured  con- 
centrations of  ice  particles,  for  the  range  of  sizes  present,  were  already 
in  the  natural  unseeded  conditions  equivalent  to  those  hoped  for  with 
seeding;  consequently,  the  silver  iodide  only  had  the  effect  of  over- 

Climax  experiments 

Following  the  initial  General  Electric  experiments,  it  was  concluded 
by  Bergeron 93  that  the  best  possibility  for  causing  considerable  rain- 
fall increase  by  artifical  means  might  be  found  in  seeding  orographic  94 
cloud  systems.  Consequently,  there  were  almost  immediate  efforts  to 
increase  orographic  precipitation,  the  greatest  concentration  of  such 
work  being  in  the  Western  United  States.  Commercial  groups  such 
as  power  companies  and  irrigation  concerns  took  the  early  initiative  in 
attempts  to  augment  snowfall  from  orographic  cloud  systems  in  order 
to  increase  streamflow  from  the  subsequent  snowmelt. 

Colorado  State  University  (CSU)  began  a  randomized  seeding 
experiment  in  the  high  Rocky  Mountains  of  Colorado  in  1960,  under 
the  direction  of  Lewis  O.  Grant,  to  investigate  snow  augmentation 
from  orographic  clouds.  The  project  was  designed  specifically  to 
(1)  evaluate  the  potential,  (2)  define  seedability  criteria,  and  (3)  de- 
velop a  technology  for  seeding  orographic  clouds  in  central  Colorado.95 
It  followed  the  1957  report  of  the  President's  Advisory  Committee  for 
Weather  Control,  in  which  it  had  been  concluded  that  seeding  of  oro- 
graphic clouds  could  increase  precipitation  by  10  to  15  percent,  basing 
this  judgment,  however,  on  data  from  a  large  number  of  seeding  pro- 
grams that  had  not  been  conducted  on  a  random  basis.96 

The  first  group  of  the  CSU  seeding  experiments  took  place  from 
1960  to  1965  in  the  vicinity  of  Climax,  Colo.,  and  has  been  designated 
Climax  I.  A  second  set  of  tests  in  the  same  area  from  1965  to  1970 
has  been  referred  to  as  Climax  II.  The  Climax  experiments  are  impor- 
tant in  the  history  of  weather  modification  because  they  were  the  first 
intensive  projects  of  their  kind  and  also  because  positive  results 
were  reported.97  The  precipitation  for  all  seeded  cases  was  greater  than 
for  all  of  the  unseeded  cases  by  9,  13,  and  39  percent,  respectively,  for 
Climax  I,  Climax  II,  and  Climax  IIB.  The  latter  set  of  data  are  a 
subsample  of  those  from  Climax  II,  from  which  possibly  contaminated 
cases  due  to  upwind  seeding  by  other  groups  were  eliminated.98 

Ibid.,  p.  30. 

93  Bergeron,  Tor,  "The  Problem  of  an  Artificial  Control  of  Rainfall  on  the  Globe ;  General 
Effects  of  Ice  Nuclei  in  Clouds."  Tellus,  vol.  1,  No.  1,  February  1949,  p.  42. 

94  A  definition  of  orographic  clouds,  a  discussion  of  their  formation,  and  a  summary  of 
attempts  to  modify  them  are  found  in  ch.  3,  p.  71  ff. 

95  Grant,  Lewis  O.,  and  Archie  M.  Kahan,  "Weather  Modification  for  Augmenting  Oro- 
graphic Precipitation."  In  Wilmot  N.  Hess  (editor),  "Weather  and  Climate  Modification," 
New  York,  Wiley,  1974,  p.  295. 

98  Advisory  Committee  on  Weather  Control.  Final  Report  of  the  Advisory  Committee  on 
Weather  Control,  Washington,  D.C.,  U.S.  Government  Printing  Office,  Dec.  31,  1957,  vol.  I, 
p.  vi.  (The  establishment  of  the  Advisory  Committee  and  its  activities  leading  to  publica- 
tion of  its  final  report  are  discussed  in  ch.  5,  under  activities  of  the  Congress  and  of  the 
executive  branch  of  the  Federal  Government,  see  pp.  195.  214,  and  236.) 

97  Byers,  "History  of  Weather  Modification,"  1974,  pp.  30-31.  „ 

98  Grant  and  Kahan,  "Weather  Modification  for  Augmenting  Orographic  Precipitation, 
1974,  p.  298. 


Lightning  suppression  experiments 

From  1947  until  the  close  of  Project  Cirrus,  interspersed  with  his 
other  activities,  Vincent  Schaefer  visited  U.S.  Forest  Service  instal- 
lations in  the  northern  Rockies  in  order  to  assist  in  attempts  to  sup- 
press lightning  by  cloud  seeding.  As  early  as  1949  an  attempt  was 
made  to  seed  thunderstorm  clouds  with  dry  ice,  dumping  it  from  the 
open  door  of  a  twin-engine  aircraft  flying  at  25,000  feet."  This 
stimulated  curiosity  among  those  involved,  but  also  showed  that  light- 
ning-prevention research  wTould  require  a  long  and  carefully  planned 
effort.  These  early  activities  led  to  the  formal  establishment  of  Proj- 
ect Skyfire  in  1953,  aimed  at  lightning  suppression,  as  part  of  the 
overall  research  program  of  the  Forest  Service.  Throughout  the  his- 
tory of  the  project,  research  benefited  from  the  cooperation  and  sup- 
port of  many  agencies  "and  scientific  groups,  including  the  National 
Science  Foundation,  the  Weather  Bureau,  Munitalp  Foundation,  the 
Advisory  Committee  on  Weather  Control,  the  National  Park  Service, 
General  Electric  Research  Laboratories,  Meteorology,  Inc.,  and  sev- 
eral universities.  The  project  was  phased  out  by  the  Forest  Service 
in  the  1970's,  since  results  of  years  of  tests  were  inconclusive,  although 
there  had  been  some  reports  of  success.  Skyfire  was  the  longest  con- 
tinuing Federal  weather  modification  research  project,  enduring  for 
about  20  years.1 

Fog  dispersal  research 

Experiments  were  conducted  on  clearing  supercooled  fog  from  run- 
ways at  Orly  Airport  in  Paris  since  1962,  using  sprays  of  liquid  pro- 
pane. Soon  after  these  successful  tests,  the  method  became  operational 
and  has  already  succeeded  in  various  U.S.  Air  Force  installations.  The 
dissipation  of  cold  fog  is  now  operational  also  at  many  locations, 
including  some  in  North  America  and  in  the  Soviet  Union.  Warm  fogs, 
however,  are  more  common  over  the  inhabited  globe,  and  efforts  to 
dissipate  them  had  not  advanced  very  far,  even  by  1970.2 

Hurricane  modification 

In  an  earlier  discussion  of  the  work  of  Langmuir  and  his  associates 
under  Project  Cirrus,  an  attempt  at  hurricane  modification  was  men- 
tioned.3 The  historical  unfolding  of  hurricane  research  in  the  United 
States  thereafter  will  not  be  reported  here  since  it  is  discussed  in  detail 
in  chapter  5,  under  Project  Stormfury,  now  a  major  weather  modifica- 
tion research  program  of  the  National  Oceanic  and  Atmospheric  Ad- 
ministration of  the  U.S.  Department  of  Commerce.4 

Hail  suppression 

The  principal  lead  in  research  to  suppress  hail  during  the  1950's  and 
1960's  was  not  in  the  United  States,  but  mainly  elsewhere,  particularly 
in  Switzerland,  France,  Italy,  tho  U.S.S.R.,  Argentina,  Bulgaria, 
Yugoslavia,  Kenya,  and  Canada.  Hail  suppression  is  based  on  the 

86  Barrows  J  S.  "Preventing  Fire  from  the  Sky."  In  U.S.  Department  of  Agriculture, 
"The  Yearbook  of  Agriculture,  1968:  Science  for  Better  Living."  Washington.  D.C.,  U.S. 
Government  Printing  Office,  1968,  p.  219. 

1  For  a  more  detailed  discussion  of  Project  Skyfire,  see  p.  309,  under  the  weather  modi- 
fication program  of  the  Department  of  Agriculture  in  ch.  r>. 

2  Byers,  "History  of  Weather  Modification,"  1974,  p.  33. 

3  See  p.  39. 

*  See  p.  296. 


hypothesis  that,  if  a  cloud  is  supplied  with  a  superabundance  of  ice 
nuclei,  the  available  water  will  be  used  to  form  a  great  number  of  snow 
crystals,  thus  depriving  the  hailstones  of  sufficient  water  to  grow 
to  damaging  size.  Most  of  the  early  foreign  attempts  to  suppress  hail 
using  explosive  rockets  or  ground-based  silver  iodide  generators 
proved  disappointing.5 

In  the  Soviet  Union,  the  Caucasus  hail  suppression  experiments  of 
the  mid-1960's  were  of  great  interest  to  cloud  physicists.  Using  radar 
to  locate  the  zone  of  greatest  water  content  in  convective  clouds  and 
rockets  with  explosive  warheads  to  deliver  lead  iodide  with  precision 
into  this  zone,  the  Russians  claimed  success  in  suppressing  hailstorms, 
based  on  statistical  reduction  in  crop  damages.  Operational  hail  sup- 
pression activity  is  now  conducted  on  a  large  scale  in  the  Soviet 
Union.6- 7  Most  hail  suppression  efforts  in  the  United  States  in  the 
1960's  were  commercial  operations  which  did  not  produce  data  of  any 
significant  value  for  further  analysis. 

Foreign  weather  modification  research 

While  the  Russians  and  some  other  countries  have  concentrated  on 
hail  suppression  research,  Australia,  like  the  United  States,  has  been 
principally  concerned  with  augmenting  precipitation.  Very  shortly 
after  Schaefer  first  seeded  a  natural  cloud  with  dry  ice,  Krauss  and 
Squires  of  the  Australian  Weather  Bureau  seeded  stratonimbus  clouds 
in  February  1947  near  Sidney.  The  Commonwealth  Scientific  and 
Industrial  Research  Organization  (CSIRO)  subsequently  organized, 
under  Dr.  E.  G.  Bowen,  what  might  then  have  been  the  world's  out- 
standing group  of  cloud  physics  and  weather  modification  scientists. 
Byers  feels  that  probably  "*  *  *  no  other  group  contributed  more  to 
practical  cloud  physics  during  the  period  approximately  from  1950  to 
1965."  8 

The  Snowy  Mountain  project  in  Australia,  whose  object  was  to  pro- 
duce a  significant  precipitation  increase  over  the  mountains  by  silver 
iodide  seeding,  has  attracted  most  attention.  For  a  5-year  period  from 
1955  through  1959,  this  experiment  was  conducted  during  the  colder 
part  of  the  Southern  Hemisphere  year,  using  silver  iodide  dispensed 
from  aircraft.  Although  initial  experimental  reports  indicated  suc- 
cessful increases  in  precipitation  over  the  target,  the  final  1963  re- 
port after  complete  analysis  stated  that  results  were  encouraging  but 

Interesting  experiments  were  carried  out  in  Israel  during  the  1960's, 
using  airborne  silver  iodide  seeding  of  mostly  cumulus  clouds.  Statis- 
tical analysis  of  data  from  the  first  5%  years  of  tests  revealed  an  in- 
crease of  18  percent  in  rainfall.10 

A  project  called  Gross versuch  III  was  conducted  on  the  southern 
slopes  of  the  Alps  in  Switzerland.  Although  initiated  as  a  randomized 
hail  suppression  experiment,  using  ground-based  silver  iodide  gen- 
erators, the  analysis  indicated  that  hail  frequency  was  greater  on 

5  Byers,  "Histry  of  Weather  Modification,"  pp.  31-32. 

6  Ibid.,  p.  32. 

7  The  hail  suppression  efforts  of  the  U.S.S.R.  are  discussed  in  more  detail  under  the  status 
of  hail  suppression  technology  in  ch.  3,  p.  88,  and  under  foreign  programs  in  ch.  9,  412. 

8  Byers,  "History  of  Weather  Modification,"  1974,  p.  23. 

9  Ibid.,  pp.  23-24. 
"  Ibid.,  p.  31. 


seeded  than  on  nonseeded  days,  but  that  the  average  rainfall  on  seeded 
days  was  21  percent  greater  than  on  nonseeded  days.11 


In  the  weeks  and  months  following  Schaefer's  first  cloud  seeding 
experiment  public  interest  grew,  and  Langmuir  and  Schaefer  spoke 
before  and  consulted  with  groups  of  water  users,  farmers  and  ranchers, 
city  officials,  Federal  program  directors,  and  scientific  societies.  As  a 
result  there  was  a  burgeoning  of  new  cloud-seeding  efforts  initiated  by 
commercial  operators,  industrial  organizations,  water  districts,  and 
groups  of  farmers.  Some  used  ground  generators  for  dispensing  silver 
iodide  obviating  the  need  for  airplanes  and  their  attendant  high  costs, 
so  that  many  such  opepations  became  quite  profitable.  Many  rain- 
makers were  incompetent  and  some  were  unscrupulous,  but  their  activi- 
ties flourished  for  a  while,  as  the  experiments  of  Shaefer  and  Lang- 
muir were  poorly  imitated.  Some  of  the  more  reliable  companies  are 
still  in  business  today,  and  their  operations  have  provided  data  valu- 
able to  the  development  of  weather  modification  technology.12 

Byers  relates  a  few  instances  of  early  commercial  operations  of 
particular  interest.13  In  1949-50  the  city  of  New  York  hired  Dr.  Wal- 
lace E.  Howell,  a  former  associate  of  Langmuir,  to  augment  its  water 
supply  by  cloud  seeding.  New  York's  citizenry  became  interested  and 
involved  in  discussions  over  Howell's  activities  as  the  news  media  made 
them  known.  This  project  was  also  the  first  case  where  legal  action  was 
taken  against  cloud  seeding  by  persons  whose  businesses  could  be 
adversely  affected  by  the  increased  rain.  Although  rains  did  come  and 
the  city  reservoirs  were  filled,  Howell  could  not  prove  that  he  was  re- 
sponsible for  ending  the  drought.14  Howell  subsequently  seeded  in 
Quebec  in  August  1953  in  an  attempt  to  put  out  a  forest  fire  and  in 
Cuba  to  increase  rainfall  for  a  sugar  plantation  owner.15 

The  Santa  Barbara  project  in  California,  also  a  commercial  opera- 
tion designed  to  increase  water  supply,  received  a  great  deal  of  atten- 
tion. In  this  period  water  was  increased  through  augmenting  rain  and 
snow  in  the  mountains  north  and  northeast  of  the  city.  The  project 
was  evaluated  by  the  California  State  Water  Resources  Board  and 
was  unique  among  commercial  contract  operations,  inasmuch  as  the 
clients  permitted  randomization  (that  is,  random  selection  of  only 
some  storms  for  seeding)  in  order  to  allow  adequate  evaluation.16 

In  the  West  the  earliest  commercial  operations  were  developed 
under  Dr.  Irving  P.  Krick,  formerly  head  of  the  Department  of  Mete- 
orology at  the  California  Institute  of  Technology.  Asked  to  monitor 
aerial  dry  ice  seeding  over  Mt.  San  Jacinto  in  1947,  Krick  became 
interested  in  weather  modification,  left  Caltech,  and  formed  his  own 
company.  Seeding  projects  were  carried  out  during  1948  and  1949  for 
ranchers  in  San  Diego  County,  Calif.,  in  Mexico,  and  in  Arizona.  In 
1050  lie  moved  to  Denver  and  formed  a  new  company,  which  began 
seeding  activity  over  the  Great  Plains,  elsewhere  in  the  West,  and  in 

"  Ibid. 

12  Ibid.,  pp.  17,  21.  22. 
"  Ibid.,  pp.  22-23. 
w  Ibid.,  p.  22. 

15  Hnlacv.  "The  Weather  Chancers, "  1968,  pp.  96-97. 
"Ibid.,  pp.  22-23. 


other  countries.  A  number  of  former  students  of  Krick  joined  him  or 
formed  other  cloud  seeding  companies,  mostly  in  the  West  during  the 
1950's.17  By  1953  Krick  had  operated  150  projects  in  18  States  and  6 
foreign  countries  and  amassed  over  200,000  hours  of  seeding  time.  For 
three  winters — 1949,  1950,  and  1951 — his  company  claimed  that  they 
had  increased  the  snowpack  in  the  Rockies  around  Denver  from  175  to 
288  percent  over  the  average  of  the  previous  10  years.  After  6  months 
of  seeding  in  Texas  in  1953,  the  water  in  a  drainage  basin  near  Dallas 
had  increased  to  363  percent  of  the  January  1  level,  while  in  nearby 
nonseeded  basins  water  ranged  from  a  22-percent  deficit  to  an  increase 
of  19  percent.18 

At  the  start  of  extensive  seeding  in  the  early  1950's  there  was  a  sharp 
increase  in  commercial  operations,  accompanied  by  great  publicity  as 
drought  began  in  the  Great  Plains.  During  the  middle  and  latter  1950's, 
however,  seeding  diminished  as  did  the  drought.  The  some  30  annual 
seeding  projects  in  the  United  States  during  the  mid  and  latter  1950's 
and  the  1960's  (excluding  fog  clearing  projects)  were  conducted  for 
the  most  part  by  about  five  firms,  on  whose  staffs  there  were  skilled 
meteorologists,  cloud  physicists,  and  engineers  for  installing  and  main- 
taining ground  and  air  systems.  Most  of  these  projects  were  in  the 
categories  of  enhancing  rain  or  snowfall,  with  a  distribution  in  a 
typical  year  as  follows :  About  a  dozen  in  the  west  coast  States,  half 
a  dozen  in  the  Rocky  Mountains-Great  Basin  area,  half  a  dozen  in 
the  Great  Plains,  and  the  remainder  in  the  rest  of  the  United  States. 
Of  the  projects  in  the  West,  six  to  nine  have  been  watershed  projects 
sponsored  by  utility  companies.  Most  of  these  projects  endured  for 
long  periods  of  years  and  many  are  still  underway.19 

Fleagle  notes  that  by  the  early  1950's,  10  percent  of  the  land  area 
of  the  United  States  was  under  commercial  seeding  operations  and 
$3  million  to  $5  million  was  being  expended  annually  by  ranchers, 
towns,  orchardists,  public  utilities,  and  resort  operators.  The  extent 
of  such  commercial  operations  receded  sharply,  and  by  the  late  1950's 
business  was  only  about  one-tenth  or  less  than  it  had  been  a  decade 
earlier.  As  noted  above,  public  utilities  were  among  those  who  con- 
tinued to  sponsor  projects  throughout  this  period.20 

Figure  1  shows  the  purposes  of  weather  modification  operations  for 
various  sections  of  the  United  States  for  the  period  July  1950  through 
June  1956.  For  each  geographical  section  the  column  graphs  represent 
the  percentage  of  the  total  U.S.  seeding  for  each  of  five  purposes  that 
was  performed  in  that  section.  The  bar  graph  in  the  inset  shows  the 
percentage  of  total  U.S.  cloud-seeding  effort  that  is  undertaken  for 
each  of  these  five  purposes.  Figure  2  shows  the  total  area  coverage 
and  the  percent  of  U.S.  territory  covered  by  cloud  seeding  for  each 
year  from  July  1950  through  June  1956.  Both  figures  are  from  the 
final  report  of  the  President's  Advisory  Committee  on  Weather 

17  Elliott,  Robert  D.,  "Experience  of  the  Private  Sector,"  1974,  p.  47. 

18  Halacy,  "The  Weather  Changers,"  1968,  p.  96. 

19  Elliott,  "Experience  of  the  Private  Sector,"  1974,  p.  46-48. 

20  Fleagle,  "Background  and  Present  Status  of  Weather  Modification."  1968,  p.  11. 

21  Advisory  Committee  on  Weather  Control,  Final  Report,  1958,  vol.  II.  Figures  lacing 
p.  242  and  243. 

Figure  1 — Purposes  of  weather  modification  operations  conducted  in  various 
geographical  sections  of  the  United  States,  July  1950  through  June  1956.  (From 
Final  Report  of  the  Advisory  Committee  on  Weather  Control,  1958.) 




1950-  1951-  1952-  1953-  (954-  1935- 

1951  1952  1953  1954  1955  1936 

Figure  2. — Total  area  coverage  and  percent  of  area  coverage  for  the  48  cotermi- 
'  nous  States  of  the  United  States  by  weather  modification  operations  for  each 

year,  July  1950  through  June  1956.  (From  Final  Report  of  the  Advisory 

Committee  on  Weather  Control,  1958.) 

Table  1  is  a  summary  of  weather  modification  operations  for  fiscal 
years  1966,  1967,  and  1968,  compiled  by  the  National  Science  Founda- 
tion from  field  operators'  reports  which  the  Foundation  required  to  be 
filed.  Figure  3  shows  the  locations  in  the  continental  United  States  for 
both  operational  and  research  weather  modification  projects  during 
fiscal  year  1968.  In  September  1968,  as  provided  by  Public  Law  90-407, 
the  National  Science  Foundation  was  no  longer  authorized  to  require 
the  submission  of  reports  on  operational  weather  modification  proj- 
ects.22 Weather  modification  activities  are  now  reported  to  the  Depart- 
ment of  Commerce,  under  provisions  of  Public  Law  92-205,  and  sum- 
mary reports  of  these  activities  are  published  from  time  to  time.23 

22  See  discussions  of  this  law  and  of  the  activities  of  the  National  Science  Foundation  as 
lead  weather  modification  acency  through  September  1968.  pp  196  and  215  in  ch.  5. 

23  See  discussions  of  Public  Law  92-205  and  of  the  weather  modification  activities  report- 
ing program  in  ch.  5,  197  and  232.  The  activities  summarized  in  the  latest  available 
Department  of  Commerce  report  are  discussed  in  ch.  7  and  listed  in  app.  G. 


1966,  1967,  AND  1968  i  (FROM  NSF  TENTH  ANNUAL  REPORT  OF  WEATHER  MODIFICATION,  1968) 

Area  treated  Number  of  Number  of  Number  of 

(square  miles)  projects  States2  operators2 

Purpose  1966       1967      1968   1966   1967   1968  1966   1967   1968  1966   1967  1968 

Rain  augmentation  and  snow- 
pack  increase   61,429  62,021  53,369  35  41  37  21  20  21  22  25  23 

Hail  suppression   20,566  20,556  13,510  3  4  4  3  3  5  3  4  4 

Fog  dissipation   100  118  145  22  15  15  15  13  9  17  15  10 

Cloud  modification   19,345  28,300  18,600  9  18  8  8  12  7  8  14  6 

Lightning  suppression   314  314  314  1  1  1  1  1  1  1  1  1 

Totals...   101,744   111,383  85,938      70      79      65      30      23      25      46      44  37 

1  Data  for  fiscal  year  1968  include  reports  received  to  Sept.  1, 1968. 

2  Totals  are  not  the  sum  of  the  items  since  many  States  and  operators  are  involved  in  more  than  one  type  of  activity. 

An  early  commercial  hail  suppression  project  was  begun  in  Colorado 
in  1958.  Eventually  it  involved  5  seeding  aircraft  and  about  125 
ground-based  generators  "making  it  the  largest  single  cloud-seeding 
project  up  to  that  time.  Results  of  the  project  were  examined  at  Colo- 
rado State  University  and  presented  at  the  International  Hail  Con- 
ference in  Verona,  Italy,  in  1960.  This  project  stimulated  the  interest 
of  scientists  and  provided  historical  roots  for  what  later  was  estab- 
lished as  the  National  Hail  Research  Experiment  in  the  same  area  over 
a  decade  later  by  the  National  Science  Foundation.2'4' 25 

During  the  1960's,  clearing  of  cold  airport  fog  through  cloud  seed- 
ing became  an  operational  procedure.  Since  the  techniques  used  can 
only  be  applied  to  cold  fog,  they  were  used  at  the  more  northerly 
or  high-altitude  airports  of  the  United  States,  where  about  15  such 
projects  were  conducted,  and  are  still  underway,  each  winter.2,6 

2*  Elliott,  "Experience  of  the  Private  Sector,"  1974,  p.  48. 

23  The  National  Hail  Research  Experiment  is  discussed  in  detail  under  the  weather  modi- 
fier lion  program  ol"  the  Xationa'  Science  Foundation  in  ch.  5  ;  se  p.  274ff. 
28  Elliott,  "Experience  of  the  Private  Sector,"  1974.  pp.  48-49. 


Figure  3. — Weather  modification  projects  in  the  United  States  during  fiscal  year 
1968.  (From  NSF  Tenth  Annual  Report  on  weather  modification,  1968.) 



In  the  various  discussions  under  activities  of  the  Congress  and  the 
executive  branch  of  the  Federal  Government  in  chapter  5,  there  are 
historical  accounts  of  legislative  actions  pertinent  to  weather  modifica- 
tion, of  the  establishment  and  functioning  of  special  committees  in 
accordance  with  public  laws  or  as  directed  by  the  executive  agencies, 
and  of  the  policy  and  planning  studies  and  reports  produced  by  the 
special  committees  or  by  the  agencies.  Inclusion  of  a  separate  historical 
account  of  these  Federal  activities  at  this  point  would  be  largely  repeti- 
tive, and  the  reader  is  referred  to  the  various  sections  of  chapter  5,  in 
which  historical  developments  of  various  Federal  activities  are  un- 
folded as  part  of  the  discussions  of  those  activities. 




(By  Robert  E.  Morrison,  Specialist  in  Earth  Sciences,  Science  Policy  Research 
Division,  Congressional  Research  Service) 


Although  the  theoretical  basis  for  weather  modification  was  laid  to 
a  large  extent  during  the  1930's,  the  laboratory  and  field  experiments 
which  ushered  in  the  "modern  era"  occurred  in  1946  and  in  the  years 
immediately  thereafter.  By  1950,  commercial  cloud  seeding  had  become 
widespread,  covering  an  estimated  total  U.S.  land  area  of  about  10  per- 
cent.1 By  the  mid-1950's,  however,  it  was  apparent  that  the  funda- 
mental atmospheric  processes  which  come  into  play  in  weather 
modification  are  very  complex  and  were  far  from  being  understood.  A 
period  of  retrenchment  and  reevaluation  began,  the  number  of  com- 
mercial operators  had  decreased  dramatically,  and  weather  modifica- 
tion had  fallen  into  some  disrepute  among  many  meteorologists  and 
much  of  the  public.  A  period  of  carefully  designed  experiments  was 
initiated  about  two  decades  ago,  supported  by  increased  cloud  physics 
research  and  increasingly  more  sophisticated  mathematical  models  and 
statistical  evaluation  schemes. 

Meanwhile,  a  small  group  of  commercial  operators,  generally  more 
reliable  and  more  responsible  than  the  typical  cloud  seeder  of  the  1950 
era,  has  continued  to  provide  operational  weather  modification  services 
to  both  public  and  private  sponsors.  These  operators  have  attempted  to 
integrate  useful  research  results  into  their  techniques  and  have  pro- 
vided a  bank  of  operational  data  useful  to  the  research  community. 
The  operational  and  research  projects  have  continued  over  the  past  two 
decades,  often  in  a  spirit  of  cooperation,  not  always  characteristic  of 
the  attitudes  of  scientists  and  private  operators  in  earlier  years.  Often 
the  commercial  cloud  seeders  have  contracted  for  important  roles  in 
major  field  experiments,  where  their  unique  experiences  have  been 
valuable  assets. 

Through  the  operational  experiences  and  research  activities  of  the 
past  30  years,  a  kind  of  weather  modification  technology  has  been 
emerging.  Actually,  though  some  practices  are  based  on  common  theory 
and  constitute  the  basic  techniques  for  meeting  a  number  of  seeding 
objectives,  there  are  really  a  series  of  weather  modification  technol- 
ogies, each  tailored  to  altering  a  particular  atmospheric  phenomenon 
and  each  having  reached  a  different  state  of  development  and  opera- 
tional usefulness.  At  one  end  of  this  spectrum  is  cold  fog  clearing,  con- 
sidered to  be  operational  now,  while  the  abatement  of  severe  storms,  at 

1  Fleagle.  Robert  G.,  "Background  and  Present  Status  of  Weather  Modification."  In 
"Weather  Modification  :  Science  and  Public  Policy,"  Seattle,  University  of  Washington 
Press,  1968,  p.  11. 



the  other  extreme,  remains  in  the  initial  research  phase.  Progress  to 
date  in  development  of  these  technologies  has  not  been  nearly  so  much 
a  function  of  research  effort  expended  as  it  has  depended  on  the  funda- 
mental atmospheric  processes  and  the  ease  by  which  they  can  be  altered. 
There  is  obvious  need  for  further  research  and  development  to  refine 
techniques  in  those  areas  where  there  has  been  some  success  and  to 
advance  technology  were  progress  has  been  slow  or  at  a  virtual 


Recently,  the  following  summary  of  the  current  status  of  weather 
modification  technology  was  prepared  by  the  Weather  Modification 
Advisory  Board : 

1.  The  only  routine  operational  projects  are  for  clearing  cold  fog. 
Research  on  warm  fog  has  yielded  some  useful  knowledge  and  good 
models,  but  the  resulting  technologies  are  so  costly  that  they  are  usable 
mainly  for  military  purposes  and  very  busy  airports. 

2.  Several  long-running  efforts  to  increase  winter  snowpack  by 
seeding  clouds  in  the  mountains  suggest  that  precipitation  can  be 
increased  by  some  15  percent  over  what  would  have  happened 

3.  A  decade  and  a  half  of  experience  with  seeding  winter  clouds  on 
the  U.S.  west  coast  and  in  Israel,  and  summer  clouds  in  Florida,  also 
suggest  a  10-  to  15-percent  increase  over  "natural''  rainfall.  Hypotheses 
and  techniques  from  the  work  in  one  area  are  not  directly  transferable 
to  other  areas,  but  will  be  helpful  in  designing  comparable  experiments 
with  broadly  similar  cloud  systems. 

4.  Xumerous  efforts  to  increase  rain  by  seeding  summer  clouds  in  the 
central  and  western  parts  of  the  United  States  have  left  many  ques- 
tions unanswered.  A  major  experiment  to  try  to  answer  them — for  the 
High  Plains  area — is  now  in  its  early  stages. 

5.  It  is  scientifically  possible  to  open  holes  in  wintertime  cloud  layers 
by  seeding  them.  Increasing  sunshine  and  decreasing  energy  con- 
sumption may  be  especially  relevant  to  the  northeastern  quadrant  of 
the  United  States. 

6.  Some  $10  million  is  spent  by  private  and  local  public  sponsors  for 
cloud-seeding  efforts,  but  these  projects  are  not  designed  as  scientific 
experiments  and  it  is  difficult  to  say  for  sure  that  operational  cloud 
seeding  causes  the  claimed  results. 

7.  Knowledge  about  hurricanes  is  improving  with  good  models  of 
their  behavior.  But  the  experience  in  modifying  that  behavior  is  primi- 
tive so  far.  It  is  inherently  difficult  to  find  enough  test  cases,  especially 
since  experimentation  on  tvphoons  in  the  "Western  Pacific  has  been 
blocked  for  the  time  being  by  international  political  objections. 

8.  Although  the  Soviets  and  some  U.S.  private  oi>erators  claim  some 
success  in  suppressing  hail  by  seeding  clouds,  our  understanding  of  the 
physical  processes  that  create  hail  is  still  weak.  The  one  major  U.S. 
field  experiment  increased  our  understanding  of  severe  storms,  but 
otherwise  proved  mostlv  the  dimensions  of  what  we  do  not  vet  know. 

0.  There  have  been  many  efforts  to  suppress  lightning  by  seeding 
thunderstorms.  Our  knowledge  of  the  processes  involved  is  fair,  but 


the  technology  is  still  far  from  demonstrated,  and  the  U.S.  Forest 
Service  has  recently  abandoned  further  lightning  experiments.2 

Lewis  O.  Grant  recently  summarized  the  state  of  general  disagree- 
ment on  the  status  of  weather  modification  technology  and  its  readiness 
for  application. 

There  is  a  wide  diversity  of  opinion  on  weather  modification.  Some  believe 
that  weather  modification  is  now  ready  for  widespread  application.  In  strong 
contrast,  others  hold  that  application  of  the  technology  may  never  be  possible 
or  practical  on  any  substantial  scale.3 

He  concludes  that — 

Important  and  steady  advances  have  been  made  in  developing  technology  for 
applied  weather  modification,  but  complexity  of  the  problems  and  lack  of  ade- 
quate research  resources  and  commitment  retard  progress.4 

In  1975,  David  Atlas,  then  president  of  the  American  Meteorologi- 
cal Society,  expressed  the  following  pessimistic  opinion  on  the  status 
of  weather  modification  technology : 

Almost  no  one  doubts  the  economic  and  social  importance  of  rainfall  augmenta- 
tion, hail  suppression,  fog  dissipation,  and  severe  storm  abatement.  But  great 
controversy  continues  about  just  what  beneficial  modification  effects  have  been 
demonstrated  or  are  possible.  Claims  and  counterclaims  abound.  After  three 
decades  of  intense  research  and  operational  weather  modification  activities,  only 
a  handful  of  experiments  have  demonstrated  beneficial  effects  to  the  general 
satisfaction  of  the  scientific  community. 

To  describe  weather  modification  as  a  "technology"  is  to  encourage  misunder- 
standing of  the  state  of  the  weather  modification  art.  The  word  "technology" 
implies  that  the  major  substantive  scientific  foundations  of  the  field  have  been 
established  and.  therefore,  that  all  that  is  required  is  to  develop  and  apply  tech- 
niques. But  one  of  the  conclusions  of  the  special  AMS  study  on  cloud  physics  was 
that  "the  major  bottleneck  impeding  developments  of  useful  deliberate  weather 
modification  techniques  is  the  lack  of  an  adequate  scientific  base."  5 

At  a  1975  workshop  on  the  present  and  future  role  of  weather  modi- 
fication in  agriculture,  a  panel  of  10  meteorologists  assessed  the  ca- 
pabilities for  modifying  various  weather  and  weather-related  phenom- 
ena, both  for  the  present  and  for  the  period  10  to  20  years  in  the  fu- 
ture. Conclusions  from  this  assessment  are  summarized  in  table  1.  The 
table  shows  estimated  capabilities  for  both  enhancement  and  dissipa- 
tion, and  includes  percentages  of  change  and  areas  affected,  where 

A  recent  study  by  Barbara  Farhar  and  Jack  Clark  surveyed  the 
opinions  of  551  scientists,  all  involved  in  some  aspect  of  weather  modi- 
fication, on  the  current  status  of  various  weather  modification  technol- 

2  Weather  Modification  Advisory  Board.  "A  U.S.  Policy  to  Enhance  the  Atmospheric 
Environment."  Oct.  21,  1977.  In  testimony  by  Harlan  Cleveland  "Weather  Modification." 
he-ring  before  the  Subcommittee  on  the  Environment  arid  the  Atmosphere.  Comnrtee  on 
Science  and  Technology.  U.S.  House  of  Representatives.  95th  Cong..  1st  sess..  Oct.  26,  1977. 
Washington.  DC  U.S.  Government  Prfnt'nsr  Office.  1077.  pp.  28-30. 

3  Grant.  Lewis  0.,  "Scientific  and  Other  Uncertainties  of  Weather  Modification."  In  Wil- 
liam A.  Thomas  (editor).  "Legal  and  Scientific  Uncertainties  of  Weather  Modification.' 
Proceedings  of  a  symposium  convened  at  Duke  University,  Mar.  11-12.  1976,  by  the 
National  Conference  of  Lawyers  and  Scientists.  Durham.  N.C.,  Duke  University  Press. 
1977.  p.  7.  . 

4  Ibid.,  p.  17. 

5  Atlas.  David.  "Selling  Atmospheric  Science.  The  President's  Page."  Bulletin  of  the 
American  Meteorological  Societv.  vol.  56.  No.  7.  July  1975.  p.  6SS. 

6  Grant.  Lewis  O.  and  John  D.  Reid  (compilers).  "Workshop  for  an  Assessment  of  the 
Present  and  Potential  Role  of  Weather  Modification  in  Agricultural  Production."  Colorado 
State  Universitv.  Fort  Collins.  Colo.,  July  15-1S.  1975.  August  1975.  PB-245-633.  pp. 


ogies.7  Table  2  is  a  summary  of  the  assessments  of  the  level  of  develop- 
ment for  each  of  12  such  technologies  included  in  the  questionaire  to 
which  the  scientists  responded,  and  table  3  shows  the  estimates  of  ef- 
fectiveness for  7  technologies  where  such  estimates  are  pertinent.  Re- 
sults of  this  study  were  stratified  in  accordance  with  respondents'  af- 
filiation, specific  education,  level  of  education,  age,  and  responsibility 
or  interest  in  weather  modification,  and  tabulated  summaries  of 
opinions  on  weather  modification  in  accordance  with  these  variables  ap- 
pear in  the  report  by  Farhar  and  Clark.8 


[From  Grant  and  Reid,  1975) 

Enhancement  Dissipation 

Amount  Amount 

change  Area  change  Area 

(per-  (square  (per-  (square 

Modified  variable          Now       10  to  20  yr      cent)  miles)  Now      10  to  20  yr       cent)  miles) 

I.  Clouds: 

1.  Cold  stratus   No  (8) 

2.  Warm  stratus   No  (10) 

3.  Fog,  cold  Yes  (10) 

4.  Fog,  warm  Yes  (10) 

5.  Fog,  artifical  (for 

temperature  con- 
trol)  Yes  (10) 

6.  Contrails  Yes  (10) 

7.  Cirrus...   Yes  (5) 

8.  Carbon  black   No  (10) 

9.  Aerosol    Yes  (7) 

II.  Convective  precipitation: 

1.  Isolated  small   Yes  (7) 

2.  Isolated  large   No  (6) 

3.  Squall  lines   Yes  (5) 

4.  Nocturnal   Yes  (5) 

5.  Imbedded  cyclonic. .  Yes  (9) 

6.  Imbedded  Oro- 

graphic  Yes  (9) 

III.  Stratoform  precip- 

1.  Orographic  Yes  (10) 

2.  Cyclonic   No  (10) 

3.  Cloud  water  collec- 

tion Yes  (10) 

IV.  Hazards: 

1.  Hail   Yes  (5) 

2.  Lightning   Yes  (7) 

3.  Erosion— wind 

gradient   No  (10) 

4.  Erosion— water 

drop  size   Yes  (5) 

5.  Wind— hurricane         No  (5) 

6.  Tornado.   No  (10) 

7.  Blowdown    No  (5) 

8.  Floods— symoptic  ...  No  (10) 

9.  Floods— mesoscale...  No  (9) 

10.  Drought   No  (10) 

V.  Other: 

1.  Albedo   Yes  (5) 

2.  Surface  roughness...  No  (6) 

3.  Topography  changes.  No  (6) 

Yes  (7)    1-1000 

No  (5)    

Yes  (10)    1-10 

Yes  (10)   1-100 

Yes  (10)   1-10 

Yes (10)    100-1000 

Yes (10)    100-1000 

No  (6)    

Yes  (10)   

Yes (10)    100  10-100 
Yes (7)     15  100-1000 
Yes(S)     20  100-10,000 
Yes  (6)      100  100-1000 
Yes  (10)    30  300-6000 

Yes (10)    20  300-6000 

Yes  (10)  Yes  (10)   1-1000 

No  (8)  Yes  (9)  

Yes  (10)  Yes  (10)    1-1000 

Yes  (10)  Yes  (10)  1-1 

N/A  N/A 

No  (10)  No  (10)    

No  (10)  No  (8)    

N/A  N/A  

N/A  N/A  

Yes  (5)  Yes  (8)     100  10-100 

Yes (5)  Yes (8)      15  10-1000 

No  (8)  Yes  (5)     20  100-10,000 

No  (8)  Yes  (5)      100  100-1000 

Yes  (8)  Yes  (10)    <5  300-6000 

Yes (8)  Yes (10)    20  300-6000 

Yes (10)  10  100-3000  Yes (10)  Yes (10)  10  100-3000 
No  (6)   No  (10)     No  (6)   

Yes (10)  .... 

Yes  (7)  (i) 

Yes  (9)  (■) 

No(10)  .... 


100-60,000  Yes 
40,000         Yes  (7) 


Yes  (9) 


No  (10)     No  (10) 

Yes  (7)  0)         10,000          Yes  (5) 

Yes  (6)    No  (6) 

Yes  (5)    No  (10) 

Yes  (5)     No  (9) 

No  (10)     No  (10) 

Yes  (6)    No  (9) 

No  (10)    Yes  (5) 

Yes  (7)    10,000 

Yes (6)  

Yes (5)  

Yes  (5)  

No  (3)   

Yes  (6)    

Yes  (6)   

Yes (10) 
Yes  (6) 
Yes  (5) 

Yes  (5) 
No  (6) 
No  (6) 

Yes (10)   

Yes  (6)    

Yes (5)   10-100 

1  Uncertain. 

7  Farhar.  Barbnra  C.  and  Jack  A.  Clark.  "Can  Wp  Modify  the  Weather?  a  Survey  of 
Scientists  "  Final  report,  vol.  3  (draft),  Institute  of  Behavioral  Science.  University  of  Colo- 
rado. Boulder,  Colo..  January  1078.  (Based  on  research  supported  by  the  National  Science 
Foundation  under  grants  No*.  ENV74-1R013  AOS.  01-35452,  GI-44087.  and  BRT74-18613, 
as  part  of  "A  Comparative  Analysis  of  Public  Support  of  and  Resistance  to  Weather  Modi- 
fication Projects.")  89  pp. 

*  Ibid. 



[From  Farhar  and  Clark,  1978] 

Operations1   Research  2      Neither     Don't  know  Other 







Weather  modification  technology 












Cold  fog  dispersal  












Precipitation    enhancement,    winter  oro- 



1 1 
1 1 




Precipitation    enhancement,    winter  oro- 

graphic, maritime  











Hail  suppression   











Precipitation  enhancement,  summer  convec- 

tive,  continental   .  











Precipitation  enhancement,  summer  convec- 

tive,  maritime  











Warm  fog  dispersal...  











Precipitation  enhancement  with  hail  sup- 













Precipitation  enhancement,  general  storms.. 












Lightning  suppression  












Hurricane  suppression  












Severe  storm  mitigation   












1  This  category  is  a  combination  of  two  responses:  "The  technology  is  ready  for  operational  application"  and  "The 
technology  can  be  effectively  applied;  research  should  continue." 

2  This  category  is  a  combination  of  two  responses:  "The  technology  is  ready  for  field  research  only"  and  "The  technology 
should  remain  at  the  level  of  laboratory  research." 




In  a  previous  review  of  weather  modification  for  the  Congress,  three 
possible  classifications  of  activities  were  identified — these  classifica- 
tions were  in  accordance  with  (1)  the  nature  of  the  atmospheric  proc- 
esses to  be  modified,  (2)  the  agent  or  mechanism  used  to  trigger  or 
bring  about  the  modification,  or  (3)  the  scale  or  dimensions  of  the 
region  in  which  the  modification  is  attempted.9  The  third  classifica- 
tion was  chosen  in  that  study,  where  the  three  scales  considered  were 
the  microscale  (horizontal  distances,  generally  less  than  15  kilometers) , 
the  mesoscale  (horizontal  distances  generally  between  15  and  200 
kilometers),  and  the  macroscale  (horizontal  distances  generally 
greater  than  200  kilometers).10  Examples  of  modification  of  processes 
on  each  of  these  three  scales  are  listed  in  table  4,  data  in  which  are 
from  Hartman.11  Activities  listed  in  the  table  are  illustrative  only, 
and  there  is  no  intent  to  indicate  that  these  technologies  have  been 
developed,  or  even  attempted  in  the  case  of  the  listed  macroscale 


[Information  from  Hartman,  19661 
Scale  Horizontal  dimensions  Examples  of  modification  processes 

Microscale   Less  than  15  km  

Mesoscale   15  to  200  km.  

Macroscale  Greater  than  200  km. 

Modification  of  human  microclimates. 
Modification  of  plant  microclimates. 
Evaporation  suppression. 
Fog  dissipation. 
Cloud  dissipation. 
Hail  prevention. 

Precipitation  through  individual  cloud  modification. 

Precipitation  from  cloud  systems. 

Hurricane  modification. 

Modification  of  tornado  systems. 

Changes  to  global  atmospheric  circulation  patterns. 

Melting  the  Arctic  icecap. 

Diverting  ocean  currents. 

In  this  chapter  the  characteristics  and  status  of  weather  modifica- 
tion activities  will  be  classified  and  discussed  according  to  the  nature 
of  the  processes  to  be  modified.  This  seems  appropriate  since  such  a 
breakdown  is  more  consonant  with  the  manner  the  subject  has  been 
popularly  discussed  and  debated,  and  it  is  consistent  with  the  direc- 
tions in  which  various  operational  and  research  activities  have  moved. 
Classification  by  the  second  criterion  above,  that  is,  by  triggering 
agent  or  mechanism,  focuses  on  technical  details  of  weather  modi- 
fication, not  of  chief  interest  to  the  public  or  the  policymaker,  although 
these  details  will  be  noted  from  time  to  time  in  connection  with  dis- 
cussion of  the  various  weather  modification  activities. 

In  the  following  major  section,  then,  discussion  of  the  principles 
and  the  status  of  planned  weather  modification  will  be  divided  accord- 

9  Hartman.  Lawton  M..  "Characteristics  and  Scope  of  Weather  Modification.  In  U.S. 
Congress,  Senate  Committee  on  Commerce.  "Weather  Modification  and  Control,"  TV  ashing- 
ton.  D.C.,  U.S.  Government  Printing  Office.  1966.  (89th  Cone:..  2d  sess.,  Senate  Kept.  JSo. 
1139.  prepared  by  the  Legislative  Reference  Service,  Library  of  Congress),  p.  20. 

10  Ibid. 

"  Ibid.,  pp.  21-31. 

34-857  O  -  79  -  7 


ing  to  the  major  broad  categories  of  phenomena  to  be  modified;  these 
will  include : 

Precipitation  augmentation. 

Hail  suppression. 

Fog  dissipation. 

Lightning  suppression. 

Severe  storm  mitigation. 
In  subsequent  major  sections  of  this  chapter  there  are  reviews  of 
some  of  the  specific  technical  problem  areas  common  to  most  weather 
modification  activities  and  a  summary  of  recommenced  research 

In  addition  to  the  intentional  changes  to  atmospheric  phenomena 
discussed  in  this  chapter,  it  is  clear  that  weather  and  climate  have  also 
been  modified  inadvertently  as  the  result  of  man's  activities  and  that 
modification  can  also  be  brought  about  through  a  number  of  natur- 
ally occurring  processes.  These  unintentional  aspects  of  weather  and 
climate  modification  will  be  addressed  in  the  following  chapter  of 
this  report.12 

Principles  and  Status  of  Weather  Modification  Technologies 

Before  discussing  the  status  and  technologies  for  modification  of 
precipitation,  hail,  fog,  lightning,  and  hurricanes,  it  may  be  useful  to 
consider  briefly  the  basic  concepts  of  cloud  modification.  The  two  major 
principles  involved  are  (1)  colloidal  instability  and  (2)  dynamic  ef- 
fects. Stanley  Changnon  describes  how  each  of  these  principles  can 
be  effective  in  bringing  about  desired  changes  to  the  atmosphere : 13 

Altering  colloidal  stability. — The  physical  basis  for  most  weather  modification 
operations  has  been  the  belief  that  seeding  with  certain  elements  would  produce 
colloidal  instability  in  clouds,  either  prematurely,  to  a  greater  degree,  or  with 
greater  efficiency  than  in  nature.  Most  cloud  seeding  presumes  that  at  least  a  por- 
tion of  the  treated  cloud  is  supercooled,  that  nature  is  not  producing  any  or 
enough  ice  at  that  temperature  of  the  cloud,  and  that  treatment  with  chemical 
agents  of  refrigerants  will  change  a  proportion  of  the  cloud  to  ice.  The  resultant 
mixture  of  water  and  ice  is  unstable  and  there  is  a  rapid  deposition  of  water 
vapor  upon  the  ice  and  a  simultaneous  evaporation  of  water  from  the  super- 
cooled droplets  in  the  cold  part  of  the  cloud.  The  ice  crystals  so  formed  become 
sufficiently  large  to  fall  relative  to  remaining  droplets,  and  growth  by  collection 
enhances  the  probability  that  particles  of  ice  or  water  will  grow  to  be  large 
enough  to  fall  from  the  cloud  and  become  precipitation. 

This  process  of  precipitation  enhancement  using  ice  nucleants  has  been  dem- 
onstrated for  the  stratiform  type  cloud,  and  generally  for  those  which  are  oro- 
graphically-produced  and  supercooled.  Cumulus  clouds  in  a  few  regions  of  the 
United  States  have  also  been  examined  for  the  potential  of  colloidal  instability  in 
their  supercooled  portions.  This  has  been  founded  on  beliefs  that  precipitation 
(1)  can  be  initiated  earlier  than  by  natural  causes,  or  (2)  can  be  produced  from 
a  cloud  which  was  too  small  to  produce  precipitation  naturally. 

Seeding  in  the  warm  portion  of  the  cloud,  or  in  "warm  clouds"  (below  the 
freezing  level),  has  also  been  attempted  so  as  to  alter  their  colloidal  instability. 
Warm-cloud  seeding  has  primarily  attempted  to  provide  the  large  droplets  neces- 
sary to  initiate  the  coalescence  mechanism,  and  is  of  value  in  clouds  where  insuffi- 
cient large  drops  exist.  In  general  alteration  of  the  coalescence  process  primarily 
precipitates  out  the  liquid  water  naturally  present  in  a  cloud,  whereas  the  ice- 
crystal  seeding  process  also  causes  a  release  of  latent  energy  that  conceivably 
results  in  an  intensification  of  the  storm,  greater  cloud  growth,  and  additional 

Alirrhifj  cloud  dynamics. — The  effects  to  alter  the  colloidal  instability  of 
clouds,  or  their  microphysical  processes,  have  been  based  on  the  concept  of  rain 

1L'  Sof  p.  145. 

13  Chnncrnon.  Stanley  A..  Jr.  "Prosont  and  Future  of  Woathor  Modification  ;  Peprtonal 
Issues."  The  Journal  of  Woathor  Mortification,  vol.  7.  No.  1,  April  1075,  pp.  154-156. 


increase  through  increasing  the  precipitation  efficiency  of  the  cloud.  Simpson 
and  Dennis  (1972)  showed  that  alterations  of  cloud  size  and  duration  by  "dynam- 
ic modification"  could  produce  much  more  total  rainfall  than  just  altering  the 
precipitation  efficiency  of  the  single  cloud.  In  relation  to  cumulus  clouds, 
"dynamic  seeding"  simply  represents  alteration  one  step  beyond  that  sought 
in  the  principle  of  changing  the  colloidal  stability.  In  most  dynamic  seeding 
efforts,  the  same  agents  are  introduced  into  the  storm  but  often  with  a  greater 
concentration,  and  in  the  conversion  of  wrater  to  ice,  enormous  amounts  of 
latent  heat  are  hopefully  released  producing  a  more  vigorous  cloud  which  will 
attain  a  greater  height  with  accompanying  stronger  updrafts,  a  longer  life,  and 
more  precipitation.  Seeding  to  produce  dynamic  effects  in  cloud  growth,  whether 
stratiform  or  cumuliform  types,  is  relatively  recent  at  least  in  its  serious  in- 
vestigation, but  it  may  become  the  most  important  technique.  If  through  con- 
trolled cloud  seeding  additional  uplift  can  be  produced,  the  productivity  in  terms 
of  rainfall  will  be  higher  whether  the  actual  precipitation  mechanism  involved 
is  natural  or  artificial. 

It  has  been  proposed  that  the  selective  seeding  of  cumulus  clouds  also  can 
either  (a)  bring  upon  a  merger  of  twTo  or  more  adjacent  clouds  and  a  much 
greater  rainfall  production  through  a  longer-lived,  larger  cloud  *  *  *  or  (b)  pro- 
duce eventually  an  organized  line  of  clouds  (through  selective  seeding  of  ran- 
domized cumulus).  The  latter  could  allegedly  be  accomplished  by  minimizing  and 
organizing  the  energy  into  a  few  vigorous  systems  rather  than  a  larger  number  of 
isolated  clouds. 

Essentially,  then,  dynamic  seeding  is  a  label  addressed  to  processes  involved 
in  altering  cloud  microphysics  in  a  selective  and  preferential  way  to  bring 
upon  more  rainfall  through  an  alteration  of  the  dynamical  properties  of  the 
cloud  system  leading  to  the  development  of  stronger  clouds  and  mesoscale 
systems.  Actually,  dynamic  effects  might  be  produced  in  other  ways  such  as 
alterations  of  the  surface  characteristics  to  release  heat,  by  the  insertion  of 
chemical  materials  into  dry  layers  of  the  atmosphere  to  form  clouds,  or  by  re- 
distribution of  precipitation  through  microphysical  interactions  in  cloud  processes. 

The  various  seeding  materials  that  have  been  used  for  cloud  modi- 
fication are  intended,  at  least  initially,  to  change  the  microphysical 
cloud  structure.  Minute  amounts  of  these  materials  are  used  with  the 
hope  that  selected  concentrations  delivered  to  specific  portions  of  the 
cloud  will  trigger  the  desired  modifications,  through  a  series  of  rapid 
multiplicative  reactions.  Seeding  materials  most  often  used  are  classi- 
fied as  (1)  ice  nuclei,  intended  to  enhance  nucleation  in  the  super- 
cooled part  of  the  cloud,  or  (2)  hygroscopic  materials,  designed  to 
alter  the  coalescence  process.14 

Glaciation  of  the  supercooled  portions  of  clouds  has  been  induced 
by  seeding  with  various  materials.  Dry  ice  injected  into  the  subfreezing 
part  of  a  cloud  or  of  a  supercooled  fog  produces  enormous  numbers  of 
ice  crystals.  Artificial  ice  nuclei,  with  a  crystal  structure  closely  re- 
sembling that  of  ice,  usually  silver  iodide  smoke  particles,  can  also 
produce  glaciation  in  clouds  and  supercooled  fogs.  The  organic  fer- 
tilizer, urea,  can  also  induce  artificial  glaciation,  even  at  temperatures 
slightly  warmer  than  freezing.  Urea  might  also  enhance  coalescence  in 
warm  clouds  and  warm  fogs.  Water  spray  and  fine  particles  of  sodium 
chloride  have  also  been  used  in  hygroscopic  seeding,  intended  to  alter 
the  coalescence  process.  There  have  been  attempts  to  produce  co- 
alescence in  clouds  or  fog  using  artificial  electrification,  either  with 
chemicals  that  increase  droplet  combination  by  electrical  forces,  or 
with  surface  arrays  of  charged  wires  whose  discharges  produce  ions 
which,  attached  to  dust  particles,  may  be  transported  to  the  clouds.15 

Problems  of  cloud  seeding  technology  and  details  of  seeding  deliv- 
ery methods  are  discussed  in  a  later  section  of  this  chapter,  as  are 

14  Ibid.,  p.  156. 

15  Ibid.,  pp.  156-157. 


some  proposed  techniques  for  atmospheric  modification  that  go  beyond 
cloud  seeding.16 


The  seeding  of  clouds  to  increase  precipitation,  either  rainfall  or 
snowfall,  is  the  best  known  and  the  most  actively  pursued  weather 
modification  activity.  Changes  in  clouds  and  precipitation  in  the 
vicinity  of  cloud  seeding  operations  have  shown  unquestionaBly  that 
it  is  possible  to  modify  precipitation.  There  is  evidence,  however, 
that  such  modification  attempts  do  not  always  increase  precipitation, 
but  that  under  some  conditions  precipitation  may  actually  be  de- 
creased, or  at  best  no  net  change  may  be  effected  over  an  area.  Never- 
theless, continued  observations  of  clouds  and  precipitation,  from  both 
seeded  and  nonseeded  regions  and  from  both  experiments  and  com- 
mercial operations,  are  beginning  to  provide  valuable  information 
which  will  be  useful  for  distinguishing  those  conditions  for  which 
seeding  increases,  decreases,  or  has  no  apparent  effect  on  precipita- 
tion. These  uncertainties  were  summarized  in  one  of  the  conclusions 
in  a  recent  study  on  weather  modification  by  the  National  Academy 
of  Sciences : 17 

The  Panel  now  concludes  on  the  basis  of  statistical  analysis  of  well-designed 
field  experiments  that  ice-nuclei  seeding  can  sometimes  lead  to  more  precipita- 
tion, can  sometimes  lead  to  less  precipitation,  and  at  other  times  the  nuclei 
have  no  effect,  depending  on  the  meteorological  conditions.  Recent  evidence  has 
suggested  that  it  is  possible  to  specify  those  microphysical  and  mesophysical 
properties  of  some  cloud  systems  that  determine  their  behavior  following 
artificial  nucleation. 

Precipitation  enhancement  has  been  attempted  mostly  for  two  gen- 
eral types  of  cloud  forms,  both  of  which  naturally  provide  precipita- 
tion under  somewhat  different  conditions.  Convective  or  cumulus 
clouds  are  those  which  are  formed  by  rising,  unstable  air,  brought 
about  by  heating  from  below  or  cooling  in  the  upper  layers.  Under 
natural  conditions  cumulus  clouds  may  develop  into  cumulo-nimbus 
or  "thunderheads,"  capable  of  producing  heavy  precipitation.  Cu- 
mulus clouds  and  convective  systems  produce  a  significant  portion 
of  the  rain  in  the  United  States,  especially  during  critical  growing 
seasons.  Attempts  to  augment  this  rainfall  from  cumulus  clouds 
under  a  variety  of  conditions  have  been  underway  for  some  years 
with  generally  uncertain  success.  The  other  type  of  precipitation- 
producing  clouds  of  interest  to  weather  modifiers  are  the  orographic 
clouds,  those  which  are  formed  when  horizontally  moving  moisture- 
laden  air  is  forced  to  rise  over  a  mountain.  As  a  result  of  the  cooling 
as  the  air  rises,  clouds  form  and  precipitation  often  falls  on  the 
windward  side  of  the  mountain.  Through  seeding  operations,  there 
have  been  attempts  to  augment  precipitation  through  acceleration 
of  this  process,  particularly  in  winter,  in  order  to  increase  mountain 

Figures  1  and  2  show  regions  of  the  coterminous  United  States 
which  are  conducive  to  precipitation  management  through  seeding 
of  spring  and  summer  convective  clouds  and  through  seeding  oro- 
graphic cloud  systems,  respectively.  The  principles  of  precipitation 

16  See  pp.  115  and  129. 

17  National  Academy  of  Sciences,  National  Research  Council,  Committee  on  Atmospheric 
Sciences,  "Weather  and  Climate  Modification  :  Problems  and  Progress,"  Washington,  D.C., 
1973,  p.  4. 


enhancement  for  both  cumulus  and  orographic  clouds,  and  the  present 
state  of  knowledge  and  technology  for  such  modification,  are  dis- 
cussed in  the  following  sections. 

Figure  1. — Regions  where  preciptation  management  may  be  applied  to  enhance 
rainfall  from  spring  and  summer  showers. 

Figure  2.— Regions  where  precipitation  management  may  be  applied  to  enhance 
snowfall  from  winter  orographic  weather  systems,  thus  augmenting  spring  and 
summer  runoff  from  mountain  snowpacks. 


Currmlus  clouds 

If  air  containing  moisture  is  cooled  sufficiently  and  if  condensation 
nuclei  such  as  dust  particles  are  present,  precipitation  may  be  pro- 
duced. This  process  occurs  when  air  is  forced  to  rise  by  convection, 
so  that  the  water  vapor  condenses  into  clouds.  Cumulus  clouds  are  the 
woolly  vertical  clouds  with  a  flat  base  and  somewhat  rounded  fop, 
whose  origin  can  always  be  traced  to  the  convection  process.  They  can 
most  often  be  observed  during  the  summer  and  in  latitudes  of  high 
temperature.  When  updrafts  become  strong  under  the  proper  con- 
ditions, cumulus  clouds  often  develop  into  cumulonimbus  clouds,  the 
principal  producer  of  precipitation.  About  three-fourths  of  the  rain 
in  the  tropics  and  subtropics  and  a  significant  portion  of  that  falling 
on  the  United  States  is  provided  from  cumulus  clouds  and  convective 

The  science  of  cloud  study,  begun  in  the  1930's  and  greatly  expanded 
following  World  War  II,  includes  two  principal  aspects — cloud  micro- 
physics  and  cloud  dynamics.  Though  once  approached  separately  by 
different  groups  of  scientists,  these  studies  are  now  merging  into  a 
single  discipline.  In  cloud  physics  or  microphysics  the  cloud  parti- 
cles— such  as  condensation  and  freezing  nuclei,  water  droplets,  and  ice 
crystals — are  studied  along  with  their  origin,  growth,  and  behavior. 
Cloud  dynamics  is  concerned  with  forces  and  motions  in  clouds,  the 
prediction  of  cloud  structure,  and  the  life  cycle  of  updrafts  and  down- 

For  cloud  modification  purposes,  present  theories  of  microphysical 
processes  provide  an  ample  basis  for  field  seeding  experiments ;  how- 
ever, further  work  is  still  needed  on  laboratory  experiments,  improved 
instrumentation,  and  research  on  assumptions.  On  the  other  hand, 
the  processes  in  cloud  dynamics  are  not  completely  understood  and 
require  continued  research.19 

Most  cumulus  clouds  evaporate  before  they  have  had  opportunity 
to  produce  precipitation  at  the  Earth's  surface.  In  fact  many  clouds 
begin  to  dissipate  at  about  the  same  time  that  rain  emerges  from  their 
bases,  leading  to  the  impression  that  they  are  destroyed  by  the  forma- 
tion of  precipitation  within  them.  This  phenomenon  is  not  yet  fully 
understood.  Cumulus  clouds  have  a  life  cycle;  they  are  born,  mature, 
and  eventually  age  and  die.  Small  cumuli  of  the  trade  regions  live  only 
about  5  to  10  minutes,  while  medium-sized  ones  exist  for  about  30  min- 
utes. On  the  other  hand,  a  giant  cumulonimbus  cloud  in  a  hurricane 
or  squall  line  may  be  active  for  one  to  several  hours.  In  its  lifetime  it 
may  exchange  over  50  million  tons  of  water,  producing  heavy  rain, 
lightning,  and  possibly  hail.  At  all  times,  however,  a  cumulus  cloud 
struggles  to  exist;  there  is  a  precarious  balance  between  the  forces 
aiding  its  growth  and  its  destruction.20 

The  increasing  capability  to  simulate  cloud  processes  on  the  com- 
puter has  been  a  major  advance  toward  understanding  cloud  modifi- 
cation.  The  ways  in  which  cloud  microphysics  influences  convective 

18  Simpson  Joanne  and  Arnett  S.  Dennis,  "Cumulus  Clouds  and  Their  Modification.  In 
Wilmot  N.  Hess  (ed.),  "Weather  and  Climate  Modification."  New  York,  John  Wiley  &  Sons, 

^'^Mo'schandreas,  Demetrios  J  .  and  Irving  Leichter.  "Present  Capabilities  to  Modify 
Cumulus  Clouds."  Geomet.  Inc.  report  No.  EF-46.H.  Final  report  for  U.S.  Navy  Environ- 
mental Prediction  Research  Facility,  Mar.  :U),  1976.  p.  209.  . 

20  Simpson  and  Dennis,  "Cumulus  Clouds  and  Their  Modification,    1947,  pp.  234-23o. 


dynamics  are  not  well  documented  or  modeled,  however.  Feedback 
mechanisms  are  dynamic  and  thermodynamic.  Dynamically,  the  buoy- 
ancy is  reduced  by  the  weight  of  the  particles  formed  within  the 
cloud,  sometimes  called  "water  loading/'  Modeling  suggests  that 
thermodynamic  feedback  from  the  microphysics  can  be  even  more 
important,  as  evaporation  at  the  edges  of  the  cloud  produces  cooling 
and  thus  induces  downdrafts.  Observations  confirm  this  important 
influence  of  evaporation,  particularly  where  the  cloud  environment  is 
relatively  dry,  but  the  effect  is  minimized  in  humid  tropical  regions.21 

Cumulus  modification  experiments 

An  enormous  amount  of  energy  is  expended  in  natural  atmospheric 
processes.  As  much  energy  as  the  fusion  energy  of  a  hydrogen  super- 
bomb is  released  in  a  large  thunderstorm,  and  in  a  moderate -strength 
hurricane  the  equivalent  of  the  energy  of  400  bombs  is  converted  each 
clay.  In  his  attempt  to  modify  precipitation  from  clouds,  man  must 
therefore  look  for  some  kind  of  a  trigger  mechanism  by  which  such 
energetically  charged  activities  can  be  controlled,  since  he  cannot  hope 
to  provide  even  a  fraction  of  the  energy  involved  in  the  natural  proc- 
ess. A  major  problem  in  evaluating  modification  efforts  is  the  large 
natural  variability  in  atmospheric  phenomena.  A  cumulus  cloud  can, 
in  fact,  do  almost  anything  all  by  itself,  without  any  attempt  to  mod- 
ify its  activity  by  man.  This  high  variability  has  led  the  layman  to 
overestimate  grossly  what  has  been  and  can  be  done  in  weather  modifi- 
cation. In  designing  an  experiment,  this  variability  requires  that  there 
be  sound  statistical  controls.22 

Precipitation  is  formed  by  somewhat  different  processes  in  warm 
clouds  and  in  subfreezing  clouds.  In  the  former,  droplets  are  formed 
from  condensation  of  water  vapor  on  condensation  nuclei  and  grow 
through  collision  and  coalescence  into  raindrops.  In  subfreezing 
clouds,  such  as  the  cumuli  under  discussion,  supercooled  water  drop- 
lets are  attached  to  ice  nuclei  which  grow  into  larger  ice  particles. 
When  large  enough,  these  particles  fall  from  the  cloud  as  snow  or  sleet 
or  may  be  converted  to  rain  if  the  temperature  between  the  cloud  and 
the  Earth's  surface  is  sufficiently  warm.  Increasing  precipitation 
through  artificial  means  is  more  readily  accomplished  in  the  case  of 
the  subfreezing  clouds.  In  addition,  attempts  have  been  made  to  pro- 
mote the  merging  of  cumulus  clouds  in  order  to  develop  larger  cloud 
systems  which  are  capable  of  producing  significantly  more  precipita- 
tion than  would  be  yielded  by  the  individual  small  clouds. 

Nearly  all  cumulus  experiments  have  involved  "seeding"  the  clouds 
with  some  kind  of  small  particles.  Sometimes  the  particles  are  dis- 
persed from  the  ground,  using  air  currents  to  move  them  into  the 
clouds.  Most  often  the  materials  are  dispensed  from  aircraft,  by  releas- 
ing them  upwind  of  the  target  clouds,  by  dropping  them  into  the  cloud 
top,  by  using  the  updraft  from  beneath  the  cloud,  or  by  flying  through 
the  cloud.  Although  more  expensive,  aircraft  seeding  permits  more 
accurate  targeting  and  opportunity  for  measurements  and  observa- 
tions. In  the  Soviet  Union,  cumulus  clouds  have  been  seeded  success- 

21  Simpson.  Joanne,  "Precipitation  Augmentation  from  Cumulus  Clouds  and  Systems  : 
Scientific  and  Technical  Foundations."  1975.  Advances  in  Geophysics,  vol.  19.  Xew  York. 
Academic  Press,  1976.  pp.  10-11. 

122  Simpson  and  Dennis,  "Cumulus  Clouds  and  Their  Modification,"  1974,  pp.  240-241. 


fully  with  artillery  shells  and  rockets,  using  radar  to  locate  parts  of 
the  clouds  to  be  seeded.23 

Augmentation  of  precipitation  in  cumulus  clouds  has  been  attempted 
both  by  accelerating  the  coalescence  process  and  by  initiating  ice  parti- 
cle growth  in  the  presence  of  supercooled  water.  In  fact,  these  processes 
are  essentially  identical  in  cumuli  where  the  tops  extend  above  the 
freezing  level. 

Prior  to  the  1960's  nearly  all  supercooled  seeding  experiments  and 
operations  were  concerned  with  attempting  to  increase  precipitation 
efficiency,  based  on  consideration  of  cloud  microstructure.24  This  is 
essentially  a  static  approach,  intended  to  produce  precipitation  by  in- 
creasing the  total  number  of  condensation  nuclei,  through  the  intro- 
duction of  artificial  nuclei  injected  by  seeding  into  or  under  the  clouds. 
This  approach  has  been  moderately  successful  in  convective  storms 
with  conducive  cloud  microstructure  in  a  number  of  locations — Cali- 
fornia, Israel,  Switzerland,  and  Australia — where  clouds  are  often 
composed  of  small  supercooled  droplets,  typical  of  winter  convection 
and  of  continental  air  masses.25  On  the  other  hand,  the  large  cumulus 
clouds  originating  in  tropical  and  subtropical  ocean  regions,  which  are 
evident  over  much  of  the  eastern  United  States  during  the  summer,  are 
much  less  influenced  by  this  static  approach.  A  technique  known  as 
dynamic  seeding  has  shown  promise  in  enhancing  precipitation  from 
clouds  of  this  type. 

According  to  dynamic  seeding  philosophy,  the  strength,  size,  and 
duration  of  vertical  currents  within  the  cloud  have  stronger  control  on 
cumulus  precipitation  than  does  the  microstructure.  In  this  technique, 
first  demonstrated  in  the  1960?s,  the  seeding  provides  artificial  nuclei 
around  which  supercooled  water  freezes,  liberating  large  quantities  of 
latent  heat  of  fusion,  within  the  clouds,  causing  them  to  become  more 
buoyant  and  thus  to  grow  to  greater  heights.  This  growth  invigorates 
circulation  within  the  cloud,  causes  increased  convergence  at  its  base, 
fosters  more  efficient  processing  of  available  moisture,  and  enhances 
rainfall  through  processes  by  which  cumuli  ordinarily  produce  such 
precipitation.  Results  of  the  Florida  Area  Cumulus  Experiment 
(FACE) ,  conducted  by  the  U.S.  Department  of  Commerce,  seem  to  in- 
dicate that  dynamic  seeding  has  been  effective  in  increasing  the  sizes 
and  lifetimes  of  individual  cumuli  and  the  localized  rainfall  resulting 
from  them.20 

Success  thus  far  in  rain  enhancement  from  dynamic  seeding  of 
cumulus  has  been  demonstrated  through  seeding  techniques  applied 
to  single,  isolated  clouds.  In  addition  to  the  experiments  in  Florida, 
dynamic  seeding  of  single  clouds  has  been  attempted  in  South  Dakota, 
Pennsylvania,  Arizona,  Australia,  and  Africa,  with  results  similar  to 
those  obtained  in  Florida.27  It  appears,  however,  that  a  natural  process 
necessary  for  heavy  and  extensive  convective  rainfall  is  the  merger 
of  cloud  groups.  Thus,  this  process  of  cloud  merger  must  be  promoted 
in  order  for  cloud  seeding  to  be  effective  in  augmenting  rainfall  from 

23  Ibid.,  p.  242. 

24  Ibid.,  1974,  pp.  246-247. 

25  Ibid.,  p.  247.  ,   -  „ 

26  William  L.  Woodley.  Joanne  Simpson.  Ronald  Biondini,  and  Joyce  Berkeley.  "Rainfall 
Results.  1970-I97.r>  ;  Florida  Area  Cumulus  Experiment,"  Science,  vol.  ID'S.  No.  4280.  Feb.  2f>. 
1077.  p.  735. 

-~  Simpson  and  Dennis,  "Cumulus  Clouds  and  Their  Modification."  1974,  p.  261. 


cumulus  clouds.  The  FACE  experiment  has  been  designed  to  investi- 
gate whether  dynamic  seeding  can  induce  such  cloud  merger  and  in- 
creased rainfall.28  Area  wide  cumulus  cloud  seeding  experiments  are 
also  planned  for  the  U.S.  Department  of  the  Interior's  High  Plains 
Cooperative  program  (HIPLEX),  being  conducted  in  the  Great 
Plains  region  of  the  United  States.29  30  There  has  been  some  indication 
that  desired  merging  has  been  accomplished  in  the  Florida  experi- 
ment.31 Though  this  merging  and  other  desirable  effects  may  be 
achieved  for  Florida  cumulus,  it  must  be  established  that  such  mergers 
can  also  be  induced  for  other  connective  systems  which  are  found  over 
most  of  the  United  States  east  of  the  Great  Plains.  Changnon  notes 
that,  "The  techniques  having  the  most  promise  for  rain  enhancement 
from  convective  clouds  have  been  developed  for  single,  isolated  types 
of  convective  clouds.  The  techniques  have  been  explored  largely 
through  experimentation  with  isolated  mountain-type  storms  or  with 
isolated  semitropical  storms.  *  *  *  Weather  modification  techniques 
do  not  exist  for  enhancing  precipitation  from  the  multicellular  con- 
vective storms  that  produce  60  to  90  percent  of  the  warm  season 
rainfall  in  the  eastern  two-thirds  of  the  United  States."  32 

Effectiveness  of  precipitation  enhancement  research  and  operations 

A  major  problem  in  any  precipitation  enhancement  project  is  the 
assessment  of  whether  observed  increases  following  seeding  result  from 
such  seeding  or  occur  as  part  of  the  fluctuations  in  natural  precipita- 
tion not  related  to  the  seeding.  This  evaluation  can  be  attempted 
through  observations  of  physical  changes  in  the  cloud  system  which 
has  been  seeded  and  through  statistical  studies. 

Physical  evaluation  requires  theoretical  and  experimental  investi- 
gations of  the  dispersal  of  the  seeding  agent,  the  manner  that  seeding 
has  produced  changes  in  cloud  microstructure,  and  changes  in  gross 
characteristics  of  a  cloud  or  cloud  system.  Our  understanding  of  the 
precipitation  process  is  not  sufficient  to  allow  us  to  predict  the  magni- 
tude, location,  and  time  of  the  start  of  precipitation.  Hence,  because 
of  this  lack  of  detailed  understanding  and  the  high  natural  variability 
of  precipitation,  it  is  necessary  to  use  statistical  methods  as  well.  There 
is  a  closer  physical  link  between  seeding  and  observable  changes  in 
cloud  microstructure ;  however,  even  the  latter  can  vary  widely  with 
time  and  position  in  natural,  unseeded  clouds,  so  that  statistical  evalua- 
tion is  also  required  with  regard  to  the  measurement  of  these 

It  should  first  be  determined  whether  the  seeding  agent  reached 
the  intended  region  in  the  cloud  with  the  desired  concentration  rather 

^Woodley,  et  al..  "Rainfall  Results,  1970-1975;  Florida  Area  Cumulus  Experiment, 
1977.  p.  735. 

29  Bureau  of  Reclamation.  U.S.  Department  of  the  Interior.  "High  Plains  Cooperative 
Program  :  Progress  and  Planning  Report  No.  2,"  Denver.  March  1976.  p.  5. 

30  The  history,  purposes,  organization,  and  participants  in  the  FACE  and  HIPLEX  pro- 
grams are  discussed  along  with  other  programs  of  Federal  agencies  in  chapter  o  or  tms 
report.  _       .       L  „ 

31  William  L.  Woodley  and  Robert  I.  Sax.  "The  Florida  Area  Cumulus  Experiment :  Ka- 
tionale.  Design.  Procedures.  Results,  and  Future  Course."  U.S.  Department  of  Commerce. 
National  Oceanic  and  Atmospheric  Administration,  Environmental  Research  Laboratories. 
NOAA  technical  report  ERL  354-WMPO  6.  Boulder,  Colo.,  January  19 , 6  pp.  41-4o. 

32  Changnon,  Stanley  A..  Jr.,  "Present  and  Future  of  Weather  Modification  :  Regional 

ISS33JWarn9e7r°'jPP'"Th9e ~Deteetabilitv  of  the  Effects  of  Seeding."  In  World  Meteorological  Or- 
ganization. Weather  Modification  Programme,  position  papers  used  in  the  Preparation  of 
the  plan  for  the  Precipitation  Enhancement  Experiment  (PEP),  Precipitation  Enhancement 
Project  Report  No.  2.  Geneva,  November  1976,  annex  I,  p.  43. 


than  spreading  into  other  areas  selected  as  controls.  When  the  agent 
has  been  delivered  by  aircraft,  this  problem  is  usually  minimized, 
though  even  in  this  case,  it  is  desirable  to  learn  how  the  material  has 
diffused  through  the  cloud.  When  ground-based  seeding  generators 
are  used,  the  diffusion  of  the  material  should  be  studied  both  by 
theoretical  studies  and  by  field  measurements.  Such  measurements 
may  be  made  on  the  seeding  agent  itself  or  on  some  trace  material 
released  either  with  the  seeding  agent  or  separately ;  this  latter  might 
be  either  a  fluorescent  material  such  as  zinc  sulphide  or  any  of  various 
radioactive  materials.  Sometimes  the  tracer  might  be  tracked  in  the 
cloud  itself,  while  in  other  experiments  it  may  be  sufficient  to  track 
it  in  the  precipitation  at  the  surface.34 

In  looking  for  cloud  changes  resulting  from  seeding,  the  natural 
cloud  behavior  is  needed  as  a  reference;  however,  since  the  character- 
istics of  natural  clouds  vary  so  widely,  it  is  necessary  to  observe  a 
number  of  different  aspects  of  the  properties  and  behavior  of  seeded 
clouds  against  similar  studies  of  unseeded  clouds  in  order  to  be  able 
^o  differentiate  between  the  two.  It  is  further  desirable  to  relate  such 
behavior  being  studied  to  predictions  from  conceptual  and  numerical 
models,  if  possible.  Direct  observations  should  be  augmented  by  radar 
studies,  but  such  studies  should  substitute  for  the  direct  measurements 
only  when  the  latter  are  not  possible.35 

A  statistical  evaluation  is  usually  a  study  of  the  magnitude  of  the 
precipitation  in  the  seeded  target  area  in  terms  of  its  departure  from 
the  expected  value.  The  expected  quantity  can  either  be  determined 
from  past  precipitation  records  or  through  experimental  controls.  Such 
controls  are  established  by  dividing  the  experimental  time  available 
roughly  in  half  into  periods  of  seeding  and  nonseeding,  on  a  random 
basis.  The  periods  may  be  as  short  as  a  day  or  be  1  or  2  weeks  in  dura- 
tion. The  precipitation  measured  during  the  unseeded  period  is  used  as 
a  measure  of  what  might  be  expected  in  the  seeded  periods  if  seeding 
hadn't  occurred.  In  another  technique,  control  areas  are  selected  where 
precipitation  is  highly  correlated  with  that  in  the  target  area  but 
which  are  never  seeded.  The  target  area  is  seeded  on  a  random  basis 
and  its  rainfall  is  compared  with  that  of  the  control  area  for  both 
seeded  and  unseeded  periods.  Another  possibility  includes  the  use  of 
two  areas,  either  of  which  may  be  chosen  for  seeding  on  a  random  basis. 
Comparisons  are  then  made  of  the  ratio  of  precipitation  in  the  lirst 
area  to  that  in  the  second  with  the  first  area  seeded  to  the  same  ratio 
when  the  second  is  also  seeded.  There  are  many  variations  of  these 
basic  statistical  designs,  the  particular  one  being  used  in  a  given  experi- 
ment depending  on  the  nature  of  the  site  and  the  measuring  facilities 
available.  As  with  the  seeding  techniques  employed  and  the  physical 
measurements  which  are  made,  experimental  design  can  only  be  final- 
ized after  a  site  has  been  selected  and  its  characteristics  studied.36 

Results  achieved  through  cumulus  modification 

Cumulus  modification  is  one  of  the  most  challenging  and  controver- 
sial areas  in  weather  modification.  In  some  cases  randomized  seeding 
efforts  in  southern  California  and  in  Israel  have  produced  significant 

Ibid.,  p.  44. 
33  Ibid. 

M  Ibid.,  p.  47). 


precipitation  from  bands  of  winter  cyclonic  storms.  However,  attempts 
have  been  less  promising  in  attributing  increased  rain  during  summer 
conditions  to  definitive  experiments.  There  has  been  some  success  in 
isolated  tropical  cumuli,  where  seeding  has  produced  an  increase  in 
cloud  height  and  as  much  as  a  twofold  to  threefold  increase  in  rain- 

In  the  Florida  area  cumulus  experiment  (FACE),  the  effects  on 
precipitation  over  a  target  area  in  southern  Florida  as  a  result  of 
seeding  cumuli  moving  over  the  area  is  being  studied  under  the  spon- 
sorship of  the  National  Oceanic  and  Atmospheric  Administration 
(NOAA).  Analysis  of  the  data  from  48  days  of  experimentation 
through  1975  provided  no  evidence  that  rainfall  over  the  fixed  target 
area  of  13,000  square  kilometers  had  been  altered  appreciably  from 
dynamic  seeding.  On  the  other  hand,  there  is  positive  evidence  for 
increased  precipitation  from  seeding  for  clouds  moving  through  the 

When  FACE  data  from  the  1976  season  are  combined  with  previous 
data,  however,  increasing  the  total  number  of  experimental  days  to  75, 
analysis  shows  that  dynamic  seeding  under  appropriate  atmospheric 
conditions  was  effective  in  increasing  the  growth  and  rain  production 
of  individual  cumulus  clouds,  in  inducing  cloud  merger,  and  in  pro- 
ducing rainfall  increases  from  groups  of  convective  clouds  as  they 
pass  through  the  target  area.  A  net  increase  seemed  to  result  from  the 
•seeding  when  rainfall  on  the  total  target  area  is  averaged.39 

Further  discussion  of  FACE  purposes  and  results  is  found  under 
the  summary  of  weather  modification  programs  of  the  Department  of 
Commerce  in  chapter  5.40 

Recent  advances  in  cumulus  cloud  modification 

In  the  past  few  years  some  major  advances  have  been  achieved  in 
cumulus  experimentation  and  in  improvement  of  scientific  under- 
standing. There  has  been  progress  in  (1)  numerical  simulation  of 
cumulus  processes  and  patterning;  (2)  measurement  techniques;  (3) 
testing,  tracing,  delivery,  and  targeting  of  seeding  materials;  and  (4) 
application  of  statistical  tools.  Recognition  of  the  extreme  difficulty  of 
cumulus  modification  and  the  increased  concept  of  an  overall  systems 
approach  to  cumulus  experimentation  have  also  been  major  advances.41 

Orographic  clouds  and  precipitation 

In  addition  to  the  convection  clouds,  formed  from  surface  heating, 
clouds  can  also  be  formed  when  moist  air  is  lifted  above  mountains 
as  it  is  forced  to  move  horizontally.  As  a  result,  rain  or  snow  may  fall, 
and  such  precipitation  is  said  to  be  orographic,  or  mountain  induced. 
The  precipitation  results  from  the  cooling  within  the  cloud  and  charac- 

37  Sax.  R.  I..  S.  A.  Changnon.  L.  O.  Grant.  W.  F.  Hitschfeld.  P.  V.  Hobbs.  A.  M.  Kanan. 
and  J.  Simnson,  "Weather  Modification:  Where  Are  We  Now  and  Where  Should  \\  e  Be 
Going?  An  Editorial  Overview."  Journal  of  Applied  Meteorology,  vol.  14.  No.  o,  August  1975, 
P-  662. 

38  Woodlev,  et  al.,  "Rainfall  Results,  1970-1975  ;  Florida  Area  Cumulus  Experiment. 
1977.  p.  742.  ,       „     . . 

^Woodley.  William  L..  Joanne  Simpson.  Ronald  Biondini.  and  Jill  Jordan.  NOAA  s 
Florida  Area  Cumulus  Experiment;  Rainfall  Results.  1970-1976  "  In  preprints  from  the 
Sixth  Conference  on  Planned  and  Inadvertent  Weather  Modification,  Champaign,  111.. 
Oct.  10-13.  1977.  Boston,  American  Meteorological  Society,  1977,  p.  209. 

40  gee  p  292 

41  Sax.  et.'  ai.  "Weather  Modification  :  Where  Are  We  Now  and  Where  Should  We  Be 
Going?  An  Editorial  Overview,"  1975,  p.  663. 


teristically  falls  on  the  windward  side  of  the  mountain.  As  the  air 
descends  on  the  leeward  side  of  the  mountain,  there  is  warming  and 
dissipation  of  the  clouds,  so  that  the  effect  of  the  mountains  is  to  pro- 
duce a  "rain  shadow"  or  desert  area.  The  Sierra  Nevada  in  western 
North  America  provide  such  conditions  for  orographic  rain  and  snow 
along  the  Pacific  coast  and  a  rain  shadow  east  of  the  mountains  when 
moisture  laden  air  generally  flows  from  the  Pacific  eastward  across 
this  range. 

The  western  United  States  is  a  primary  area  with  potential  for 
precipitation  augmentation  from  orographic  clouds.  This  region  re- 
ceives much  of  its  annual  precipitation  from  orographic  clouds  during 
winter,  and  nearly  all  of  the  rivers  start  in  the  mountains,  deriving 
their  water  from  melting  snowpacks.  The  major  limitation  on  agricul- 
ture here  is  the  water  supply,  so  that  additional  water  from  increased 
precipitation  is  extremely  valuable.  Streamflow  from  melting  snow 
is  also  important  for  the  production  of  hydroelectric  power,  so  that 
augmentation  of  precipitation  during  years  of  abnormally  low  natural 
snowfall  could  be  valuable  in  maintaining  required  water  levels  neces- 
sary for  operation  of  this  power  resource.  Orographic  clouds  provide 
more  than  90  percent  of  the  annual  runoff  in  many  sections  of  the 
western  United  States.42 

Figure  3  (a)  and  (b)  are  satellite  pictures  showing  the  contrast 
between  the  snow  cover  over  the  Sierra  Nevada  on  April  28, 1975,  and 
on  April  19, 1977.  This  is  a  graphical  illustration  of  why  much  of  Cali- 
fornia was  drought  stricken  during  1977.  The  snowpack  which  custo- 
marily persists  in  the  highest  elevations  of  the  Sierras  until  July  had 
disappeared  by  mid-May  in  1977.43 

The  greatest  potential  for  modification  exists  in  the  winter  in  this 
region,  while  requirements  for  water  reach  their  peak  in  the  summer  ; 
hence,  water  storage  is  critical.  Fortunately,  the  snowpack  provides  a 
most  effective  storage,  and  in  some  places  the  snowmelt  lasts  until  early 
July.  Water  from  the  snowmelt  can  be  used  directly  for  hydroelectric 
power  generation  or  for  irrigation  in  the  more  arid  regions,  while 
some  can  be  stored  in  reservoirs  for  use  during  later  months  or  in  sub- 
sequent dry  years.  In  some  regions  where  the  snowpack  storage  is  not 
optimum,  offseason  orographic  precipitation  is  still  of  great  value, 
since  the  water  holding  capacity  of  the  soil  is  never  reached  and  addi- 
tional moisture  can  be  held  in  the  soil  for  the  following  groAving  season. 

Orographic  clouds  are  formed  as  moist  air  is  forced  upward  hy 
underlying  terrain.  The  air  thus  lifted,  containing  water  vapor,  cools 
and  expands.  If  this  lifting  and  cooling  continue,  the  air  parcels  will 
frequently  reach  sal  mat  ion.  If  the  air  becomes  slightly  supersaturated, 
small  droplets  begin  to  form  by  condensation,  and  a  cloud  develops, 
which  seems  to  hang  over  the  mountain  peak.  The  location  where  this 
condensation  occurs  can  be  observed  visually  by  the  edge  of  the  cloud 
on  the  windward  side  of  the  mountain.  Upon  descent  in  the  lee  of  the 
mountain  the  temperature  and  vapor  capacity  of  the  air  parcel  again 

"Grant,  Lewis  O.  and  Archie  M.  Kahan,  "Weather  Modification  for  Augmenting  Oro- 
graphic Precipitation."  In  Wilmot  N.  Hess  (editor),  "Weather  and  Climate  Modification," 
New  York.  Wiley.  1974.  p.  2S5. 

4:1  U.S.  Department  of  Commerce,  news  release,  NOAA  77-234.  NO  A  A  Public  Affairs  Office, 
Rockville,  Md.,  Aug.  17,  1077. 


increase,  so  that  any  remaining  liquid  droplets  or  ice  crystals 

(a)  April  28,  1975 

Figure  3. — NOAA-3  satellite  pictures  of  the  snowcover  on  the  Sierra  Nevada 
Mountains  in  (a)  April  1975  and  (b)  April  1977.  (Courtesy  of  the  National 
Oceanic  and  Atmospheric  Administration.) 

44  Sax.  et  al..  "Weather  Mortification  :  Where  Are  We  Now  and  Where  Should  We  Be 
Going?"  an  editorial  overview,  1975,  pp.  657-658. 



(b)  April  19,  1977 

The  supercooled  cloud  droplets  exist  as  liquid  at  temperatures  down 
to  about  -20°  C ;  but  at  temperatures  colder  than  -20°  C,  small  ice 
crystals  begin  to  form  around  nuclei  that  are  naturally  present  in  the 
atmosphere.  Once  formed,  the  ice  crystals  grow  rapidly  because  the 
saturation  vapor  pressure  over  ice  is  less  than  that  over  water.  As  the 
crystals  increase  they  may  fall  and  eventually  may  reach  the  ground 
as  snow.  The  temperature  at  the  top  of  the  cloud  is  an  important 
factor  in  winter  storms  over  mountains,  since  natural  ice  crystals  will 
not  form  in  large  quantities  if  the  cloud  top  is  warmer  than  —20°  C. 
If  the  temperature  is  below  —20°  C,  however,  a  large  fraction  of  the 
cloud  particles  will  fall  as  snow  from  natural  processes.45 

45  Weisbecker,  Leo  W.  (compiler),  "The  Impacts  of  Snow  Enhancement;  Technology 
Assessment  of  Winter  Orographic  Snowpack  Augmentation  in  the  Upper  Colorado  River 
Basin,"  Norman,  Okla.,  University  of  Oklahoma  Press,  1974,  pp.  64-66. 


Orographic  precipitation  modification 

According  to  Grant  and  Kalian,  "  *  *  *  research  has  shown  that 
orographic  clouds  *  *  *  provide  one  of  the  most  productive  and 
manageable  sources  for  beneficial  weather  modification."  46  In  a  re- 
cent study  by  the  National  Academy  of  Sciences,  it  was  concluded 
broadly  that  orographic  clouds  provide  one  of  the  "main  possibilities 
of  precipitation  augmentation,*'  based  on  the  considerations  below : 47 
A  supply  of  cloud  water  that  is  not  naturally  converted  into 
precipitation  sometimes  exists  for  extended  periods  of  time ; 

Efficient  seeding  agents  and  devices  are  available  for  treating 
these  clouds; 

Seeding  agents  can  sometimes  (not  always)  be  delivered  to 
the  proper  cloud  location  in  proper  concentrations  and  at  the 
proper  time; 

Microphysical  cloud  changes  of  the  type  expected  and  neces- 
sary for  seeding  have  been  demonstrated; 

Substantial  increases  in  precipitation  with  high  statistical  sig- 
nificance have  been  achieved  in  some  well-designed  randomized 
experiments  for  clouds  that,  based  on  physical  concepts,  should 
have  seeding  potential;  and 

Augmentation  of  orographic  precipitation  can  have  great  eco- 
nomic potential. 

Although  natural  ice  crystals  will  not  form  in  sufficient  numbers  if 
the  cloud  top  is  warmer  than  —20°  C,  it  has  been  shown  that  particles 
of  silver  iodide  smoke  will  behave  as  ice  nuclei  at  temperatures  some- 
what warmer  than  —  20°  C,  so  that  ice  crystals  can  be  produced  by  such 
artificial  nuclei  in  clouds  with  temperatures  in  the  range  of  —10°  to 
—  20°  C.  Whereas  in  the  natural  state,  with  few  active  nuclei  at  these 
temperatures,  the  cloud  particles  tend  to  remain  as  water  droplets, 
introduction  of  the  silver  iodide  can  quickly  convert  the  supercooled 
cloud  into  ice  crystals.  Then,  the  natural  growth  processes  allow  the 
crystals  to  grow  to  sufficient  size  for  precipitation  as  snow.48 

Meteorological  factors  which  favor  increased  snowfall  from  oro- 
graphic clouds  through  cloud  seeding  are  summarized  by 
Weisbecker : 49 

The  component  of  the  airflow  perpendicular  to  the  mountain 
ridge  must  be  relatively  strong. 

The  air  must  have  a  high  moisture  content.  Generally,  high 
moisture  is  associated  with  above-normal  temperatures. 

The  cloud,  including  its  upper  boundary,  should  be  at  a  temp- 
erature warmer  than  — 20°  C.  Since  temperature  decreases  with 
increasing  altitude,  this  temperature  criterion  limits  the  altitude 
of  the  cloud  top.  However,  it  is  advantageous  for  the  cloud  base 
to  be  low,  since  the  water  droplet  content  of  the  cloud  will  then 
be  relatively  large. 

46  Grant  and  Kahan,  "Weather  Modification  for  Augmenting  Orographic  Precipitation," 
1974.  p.  282. 

*7  Committee  on  Climate  and  Weather  Fluctuations  and  Agricultural  Production,  National 
Research  Council,  "Climate  and  Food  ;  Climatic  Fluctuation  and  U.S.  Agricultural  Produc- 
tion." National  Academy  of  Sciences.  Washington,  D.C.,  1976,  p.  136. 

48  Weisbecker,  "The  Impacts  of  Snow  Enhancement ;  Technology  Assessment  of  Winter 
Orographic  Snowpack  Augmentation  in  the  Upper  Colorado  Basin,"  1974,  p.  66. 

» Ibid.  pp.  66-67. 


It  must  be  possible  to  disperse  silver  iodide  particles  within  the 
cloud  in  appropriate  numbers  to  serve  as  ice  crystal  nuclei.  If 
ground  generators  are  used,  the  silver  iodide  smoke  must  be  dif- 
fused by  turbulence  and  lifted  by  the  airflow  into  cloud  regions 
where  temperatures  are  colder  than  — 10°  C. 

The  ice  crystals  must  have  time  to  grow  to  a  precipitable  size 
and  to  fall  to  Earth  before  reaching  the  downdrafts  that  exist  on 
the  far  side  of  the  mountain  ridge. 
The  meteorological  conditions  which  are  ideally  suited  for  augment- 
ing artificially  the  snowfall  from  a  layer  of  orographic  clouds  are 
depicted  in  figure  4.  The  figure  also  shows  the  optimum  location  of 
ground-based  silver  iodide  smoke  generators  upwind  of  the  target  area 
as  well  as  the  spreading  of  the  silver  iodide  plume  throughout  the  cloud 
by  turbulent  mixing.  Although  there  are  several  seeding  agents  with 
suitable  properties  for  artificial  ice  nuclei,  silver  iodide  and  lead  iodide 
appear  to  be  most  effective.  Owing  to  the  poisonous  effects  of  lead  com- 
pounds, lead  iodide  has  not  had  wide  use.  The  optimum  silver  iodide 
particle  concentration  is  a  function  of  the  temperature,  moisture,  and 
vertical  currents  in  the  atmosphere ;  it  appears  to  be  in  the  range  from 
5  to  100  nuclei  per  liter  of  cloud.50  While  the  most  common  means  of 
dispersing  silver  iodide  in  mountainous  areas  is  by  ground-based  gen- 
erators, other  methods  of  cloud  seeding  make  use  of  aircraft,  rockets, 
and  balloons. 

In  contrast  to  convective  clouds,  ice  crystal  formation  in  orographic 
clouds  is  thought  to  be  static,  depending  primarily  on  cloud  micro- 
physics,  and  that  orographic  cloud  seeding  has  little  effect  on  the 
general  patterns  of  wind,  pressure,  and  temperature.  On  the  other 
hand,  clouds  formed  primarily  by  convection,  such  as  summer  cumulus 
or  hurricane  clouds,  are  believed  to  be  affected  dynamically  by  seeding 
as  noted  above  in  the  discussion  of  modification  of  convective  clouds.51 
Since  the  lifting  of  the  air  in  winter  mountain  storms  is  mainly  caused 
by  its  passage  over  the  mountain  barrier,  the  release  of  latent  energy 
accompanying  this  lifting  has  little  effect  upon  the  updraft  itself.  In 
convective  cases,  however,  heat  released  through  seeding  increases 
buoyancy  and  lifting,  with  attendant  effects  on  the  wind  and  pressure 
fields.  The  static  nature  of  the  processes  involved  in  orographic  cloud 
modification  therefore  suggests  that  there  is  less  chance  that  the  storm 
dynamics  downwind  of  the  target  area  will  be  altered  appreciably  as  a 
result  of  the  modification  activities.52 

60  Ibid.,  p.  68. 

si  See  p.  68. 

52  Ibid.,  pp.  70-71. 


Figure  4. — Idealized  model  showing  meteorological  conditions  that  should  lead 
to  increased  snowfall  if  clouds  are  seeded  with  silver  iodide  particles.  (From 
Weisbecker,  1974.) 

Orographic  seeding  experiments  and  seeddbility  criteria 

A  randomized  research  weather  modification  program  with  winter 
orographic  storms  in  central  Colorado  was  initiated  by  Colorado  State 
University  in  1959.  Data  on  precipitation  and  cloud  physics  were  col- 
lected for  16  years  under  this  Climax  program,  named  for  the  location 
of  its  target  area  near  Climax,  Colo.  Analysis  of  data  has  shown  pre- 
cipitation increases  between  100  and  200  percent  when  the  average 
temperatures  of  seeded  clouds  at  the  500  millibar  level  were  —  20°C  or 
warmer.  When  corresponding  temperatures  were  —  26°C  to  —  21°C, 
precipitation  changes  ranged  between  —5  and  +6  percent.  For  tem- 
peratures colder  than  —  26°C,  seeded  cloud  systems  produced  decreases 
in  precipitation  ranging  from  22  to  46  percent.53 

While  the  results  of  Climax  have  provided  some  useful  guidelines  in 
establishing  seedability  criteria  of  certain  cloud  systems,  it  has  been 
learned  from  other  experimental  programs  that  direct  transfer  of  the 
Climax  criteria  to  other  areas  is  not  warranted.54  In  particular,  this 
nontransferability  has  been  evident  in  connection  with  analysis  of  re- 
sults from  the  Colorado  River  Basin  Pilot  Project,  conducted  from 
1970  through  1975  in  the  San  Juan  Mountains  of  southwest  Colorado, 
sponsored  by  the  Bureau  of  .Reclamation  of  the  U.S.  Department  of 
the  Interior.55 

Difficulties  are  frequently  encountered  in  attempting  to  evaluate  ex- 
perimental cloud-seeding  programs.  A  major  problem  in  assessing 
results  of  all  cold  orographic  cloud-seeding  projects  stems  from  the 
high  natural  variability  of  cloud  properties.  Frequent  measurements 
are  therefore  required  in  order  to  monitor  these  properties  carefully 
and  consistently  throughout  the  experiment.  Another  set  of  problems 
which  have  troubled  investigators  in  a  number  of  experimental  pro- 
grams follow  from  improper  design.  Such  a  deficiency  can  easily  re- 

53Hjermstad.  Lawrence  M..  "San  Juan  and  Climax."  In  proceedings  of  Special  Weather 
Modification  Conference;  Augmentation  of  Winter  Orographic  Precipitation  in  the  West- 
ern United  States,  San  Francisco,  Nov.  11-13,  1975,  Boston,  American  Meteorological 
Society.  1975,  p.  1  (abstract). 

~4Ibid.,  pp.  7-S.  .  ... 

53  This  nroiect.  part  of  Project  Skywater  of  the  Bureau  of  Reclamation,  is  discussed  along 
with  other  programs  of  Federal  agencies  in  chapter  5  of  this  report,  see  p.  2o4. 

34-857  O  -  79  -  8 


suit,  for  example,  if  insufficient  physical  measurements  have  been  taken 
prior  to  establishment  of  the  design  of  the  experiment.56 

Under  Project  Sky  water  the  Bureau  of  Reclamation  has  carried  out 
an  analysis  of  data  from  seven  past  weather  modification  projects  in 
order  to  identify  criteria  which  define  conditions  when  cloud  seeding 
will  increase  winter  snowfall  in  mountainous  terrain  and  when  such 
seeding  would  have  no  effect  or  decrease  precipitation.  The  seven 
projects  examined  in  the  study  were  conducted  in  the  Rocky  Moun- 
tains, in  the  Sierra  Nevada,  and  in  the  southern  coast  range  in  Cali- 
fornia during  the  1960's  and  1970?s,  in  areas  which  represent  a  wide 
range  of  meteorological  and  topographical  conditions.57 

Figure  5  shows  the  locations  of  the  seven  projects  whose  results  were 
analyzed  in  the  Skywater  study,  and  table  5  includes  more  detailed 
information  on  the  locations  and  dates  of  seeding  operations  for  these 
projects.  General  seedability  criteria  derived  from  this  study  were 
common  to  all  seven  projects,  with  the  expectation  that  the  criteria 
will  also  be  applicable  to  all  winter  orographic  cloud-seeding  projects. 
While  there  have  been  other  efforts  to  integrate  results  from  several 
projects  into  generalized  criteria,  based  only  on  a  few  meteorological 
variables,  Vardiman  and  Moore  considered  11  variables  which  depend 
on  mountain  barrier  shapes  and  sizes  and  on  characteristics  of  the 
clouds.  Some  of  these  variables  are  physically  measurable  while  others 
are  derived  from  simple  computations.58 

Figure  5. — Locations  of  winter  orographic  weather  modification  projects  whose 
results  were  used  to  determine  generalized  cloud  seeding  criteria.  (From  Vardi- 
man and  Moore,  1977. 

MHobbs.  Peter  V,  "Evaluation  of  Cloud  Seeding  Experiments;  Some  Lessons  To  Be 
i.earned  From  the  Cascade  and  San  Juan  Projects."  In  proceedings  of  Special  Weather 
Modification  Conference  ;  Augmentation  of  Winter  Orographic  Precipitation  in  the  West- 
Society  1976 .      af  Francisco,  Nov.  11-13,  1975.  Boston,  American  Meteorological 

"Vardiman.  Tarry  and  James  A.  Moore.  "Generalized  Criteria  for  Seeiing  Winter  Oro- 
graphic Cloudy'  Skywater  monograph  No.  1,  U.S.  Department  of  the  Interior,  Bureau  of 
133  -Division  of  Atmospheric  Water  Resources  Management,  Denver,  July  1977. 

■  Ibid.,  p.  15. 



[From  Vardiman  and  Moore,  1977] 

Project  Site  Seeding  operations 


Bridger  Range  Project  (BGR)   Rocky  Mountains,  Montana   1969-70  to  1971-72  (3  seasons). 

Climax  Project  (CMX)    Rocky  Mountains,  Colorado   1960-61  to  1969-70  (10  seasons). 

Colorado  River  Basin  Pilot  Project  Rocky  Mountains,  Colorado    1970-71  to  1974-75  (5  seasons). 


Central  Sierra  Research  Experiment  Sierra  Nevada,  California   1968-69  to  1972-73  (5  seasons). 


Jemez  Mountains  Project  (JMZ)   Rocky  Mountains,  New  Mexico   1968-69  to  1971-72  (4  seasons). 

Pyramid  Lake  Pilot  Project  (PYR)  Sierra  Nevada,  California/Nevada          1972-73  to  1974-75  (3  seasons). 

Santa  Barbara  Project  (SBA)   Southern  Coast  Range,  California          1967-68  to  1973-74(7  seasons). 

Detailed  analyses  were  conducted  on  four  variables  calculated  from 
topography  and  vertical  distributions  of  temperature,  moisture,  and 
winds.  These  are  (1)  the  stability  of  the  cloud,  which  is  a  measure  of 
the  likelihood  that  seeding  material  will  reach  a  level  in  the  cloud 
where  it  can  effect  the  precipitation  process;  (2)  the  saturation  mixing 
ratio  a£  cloudbase,  a  measure  of  the  amount  of  water  available  for 
conversion  to  precipitation;  (3)  the  calculated  cloud  top  temperature, 
a  measure  of  the  number  of  natural  ice  nuclei  available  to  start  the 
precipitation  process;  and  (4)  the  calculated  trajectory  index,  a  meas- 
ure of  the  time  available  for  precipitation  particles  to  form,  grow,  and 
fall  to  the  ground.59 

Results  of  the  study  thus  far  are  summarized  below : 

Seeding  can  increase  precipitation  at  and  near  the  mountain  crest  under  the 
following  conditions: 

Stable  clouds  with  moderate  water  content,  cloud  top  temperatures  between 
—10  and  —30°  C,  and  winds  such  that  the  precipitation  particles  would  be 
expected  to  fall  at  or  near  the  crest  of  the  mountain  barrier. 

Moderately  unstable  clouds  with  moderate-to-high  water  content,  cloud 
top  temperatures  between  —10  and  —30°  C,  and  a  crest  trajectory  for  the  pre- 

Seeding  appears  to  decrease  precipitation  across  the  entire  mountain  barrier 
under  the  following  condition: 

Unstable  clouds  with  low  water  content,  cloud  top  temperatures  less 
than  —30°  C,  and  winds  such  that  the  precipitation  particles  would 
be  carried  beyond  the  mountain  crest  and  evaporate  before  reaching  the 

59  Bureau  of  Reclamation.  Division  of  Atmospheric  Water  Resources  Management,  "Sum- 
mary Report ;  Generalized  Criteria  for  Seeding  Winter  Orographic  Clouds.'"  Denver.  March 
1977,  p.  1.  (This  is  a  summary  of  the  report  by  Vardiman  and  Moore  which  is  referenced 
above. ) 

80  Ibid.,  pp.  1-2. 

Rime  ice  conditions  at  sensing  device  which  measures  intensity  of  snowfall. 
(Courtesy  of  the  Bureau  of  Reclamation.) 


Results  quoted  above  represent  only  a  portion  of  the  analyses  which 
are  to  be  carried  out.  Seeding  "window"  bounds  must  be  refined,  and 
the  expected  effect  must  be  converted  into  estimates  of  additional  pre- 
cipitation a  target  area  might  experience  during  a  winter  season.  It  is 
very  unlikely  that  observed  effects  could  have  occurred  by  chance  in 
view  of  the  statistical  tests  which  were  applied  to  the  data.61 

Operational  orographic  seeding  projects 

For  several  decades  commercial  seeding  of  orographic  clouds  for 
precipitation  augmentation  has  been  underway  in  the  western  United 
States,  sponsored  by  specific  users  which  include  utility  companies, 
agricultural  groups,  and  State  and  local  governments.  Much  of  the 
technology  was  developed  in  the  late  forties  and  early  fifties  by  com- 
mercial operators,  with  some  improvements  since.  The  basic  technique 
most  often  used  involves  release  of  silver  iodide  smoke,  usually  from 
ground-based  generators,  along  the  upwind  slopes  of  the  mountain 
where  clouds  are  seeded,  as  shown  schematically  in  figure  6.  It  is  the 
opinion  of  Grant  and  Kahan  that  this  basic  approach  still  appears 
sound  for  seeding  orographic  clouds  over  many  mountain  barriers,  but 
that  in  all  aspects  of  these  operating  programs,  there  have  been  "sub- 
stantial improvements"  as  a  result  of  research  and  development  pro- 
grams.62 They  summarized  the  following  major  deficiencies  of  past 
operational  orographic  seeding  programs : 

1.  The  lack  of  criteria  for  recognizing  the  seedability  of  specific 

2.  The  lack  of  specific  information  as  to  where  the  seeding 
materials  would  go  once  they  are  released. 

3.  The  lack  of  specific  information  as  to  downwind  or  broader 
social  and  economic  effects  from  the  operations. 

4.  The  lack  of  detailed  information  on  the  efficiency  of  seeding 
generators  and  material  being  used  for  seeding  clouds  with  differ- 
ing temperatures.63 

Figure  6. — Schematic  view  of  silver  iodide  generators  placed  upwind  from  a  tar- 
get area  in  the  mountains,  where  orographic  clouds  are  to  be  seeded  for  pre- 
cipitation enhancement  (From  Weisbecker,  1974.) 

61  Ibid.,  p.  2. 

63  Grant  and  Kalian,  "Weather  Modification  for  Augmenting  Orographic  Precipitation," 
1974,  p.  307. 

«  Ibid.,  pp.  307-308. 


Results  achieved  through  orographic  precipitation  modification 

Results  from  several  projects  in  the  western  United  States  have 
shown  that  winter  precipitation  increases  of  10  to  15  percent  are  pos- 
sible if  all  suitable  storms  are  seeded.64  From  randomized  experiments 
at  Climax,  Colo.,  precipitation  increases  of  70  to  80  percent  have  been 
reported.  These  results,  based  on  physical  considerations,  are  repre- 
sentative of  cases  which  have  a  high  potential  for  artificial 

64  U.S.  Department  of  the  Interior,  Bureau  of  Reclamation,  "Reclamation  Research  in  the 
Seventies,"  Second  progress  report.  A  water  resources  technical  publication  research  report 
No.  28,  Washington,  U.S.  Government  Printing  Office,  1977,  p.  2. 

65  National  Academy  of  Sciences,  "Climate  and  Food  ;  Climatic  Fluctuation  and  U.S.  Agri- 
cultural Production,"  1976,  p.  136. 




The  hail  problem 

Along  with  floods,  drought,  and  high  winds,  hail  is  one  of  the  major 
hazards  to  agriculture.  Table  6  shows  the  estimated  average  annual 
hail  loss  for  various  crops  in  the  United  States,  for  each  of  the  18 
States  whose  total  annual  crop  losses  exceed  $10  million.  Also  included 
in  the  table  are  total  losses  for  each  crop  and  for  each  of  the  18  States 
and  the  aggregate  of  the  remaining  States. 

The  following  vivid  description  of  a  hailstorm  conveys  both  a  sense 
of  its  destructiveness  and  some  notion  of  its  capricious  nature : 

At  the  moment  of  its  happening,  a  hailstorm  can  seem  a  most  disastrous  event. 
Crashing  stones,  often  deluged  in  rain  and  hurled  to  the  surface  by  wind,  can 
create  instant  destruction.  Picture  windows  may  he  broken,  cars  dented,  or  a 
whole  field  of  corn  shredded  before  our  eyes. 

Then  quite  quickly,  the  storm  is  over.  Xow  the  damage  is  before  us.  we  per- 
ceive it  to  be  great,  and  we  vow  to  do  something  to  prevent  its  happening  again. 

But  what  we  have  experienced  is  "our"  storm.  Hail  did  not  happen  perhaps  a 
mile  away.  We  may  see  another  the  same  day.  or  never  again.  Thus,  the  concept 
of  hail  suppression  is  founded  in  a  real  or  perceived  need,  but  the  assessment  of 
this  solution  must  be  considered  in  terms  of  the  nature  of  hail.06 


[In  millions  of  dollars]1 



and  veg- 













































North  Dakota.  







North  Carolina  
















South  Dakota  










































South  Carolina  











.  1 


















Other  States  


















1  1973  production  and  price  levels. 

2  Coarse  grains:  Barley,  rye,  oats,  sorghum. 

Source:  "National  Hail  Research  Experiment"  from  Boone  (1974). 

A  major  characteristic  of  hail  is  its  enormous  variability  in  time, 
space,  and  size.  Some  measure  of  this  great  variability  is  seen  in  figure 
7,  which  shows  the  average  annual  number  of  days  with  hail  at  points 
within  the  continental  United  States.  The  contours  enclose  points  with 
equal  frequency  of  hail  days.67 

00  Chanson,  Stanley  A..  Jr..  Ray  Jay  Davis,  Barbara  C.  Farhar.  J.  Eupene  Haas,  J. 
Lorena  Ivens.  Marvin  V.  Jones,  Donald  A.  Klein,  Dean  Mann.  Griffith  M.  Morgan.  Jr..  Steven 
T.  Sonka.  Earl  R.  Swanson.  C.  Robert  Taylor,  and  Jon  Van  Blokland.  "Hail  Suppression  : 
Impacts  and  Issues."  Final  report — "-Technology  Assessment  of  the  Suppression  of  Hail 
fTASH ) ."  Urbana,  111..  Illinois  State  Water  Survey.  April  lt>77  (sponsored  by  the  National 
Science  Foundation,  Research  Applied  to  National  Needs  Program),  p.  9. 

«  Ibid. 


Hail  forms  in  the  more  active  convective  clouds,  with  large  vertical 
motions,  where  large  quantities  of  water  vapor  condense  under  condi- 
tions in  which  large  ice  particles  can  grow  quickly.  The  kinds  of  con- 
vective clouds  from  which  hail  can  be  formed  include  (1)  supercells 
(large,  quasi-steady-state,  convective  storms,  (2)  multicell  storms 
(active  convective  storms  with  multiple  cells),  (3)  organized  convec- 
tive storms  of  squall  lines  or  fronts,  and  (4)  unstable,  highly  convective 
small  cumuli  (primarily  occurring  in  spring). 68  While  hail  generally 
occurs  only  in  thunderstorms,  yet  only  a  small  proportion  of  the  world's 
thunderstorms  produce  an  appreciable  amount  of  hail.  Based  upon  sev- 
eral related  theories,  the  following  desciption  of  the  formation  of  hail 
is  typical : 

Ice  crystals  or  snowflakes,  or  clumps  of  snowflakes,  which  form  above  the 
zone  of  freezing  during  a  thunderstorm,  fall  through  a  stratum  of  supercooled 
water  droplets  (that  is,  water  droplets  well  below  0°  O).  The  contact  of  the  ice 
or  snow  particles  with  the  supercooled  water  droplets  causes  a  film  of  ice  to  form 
on  the  snow  or  ice  pellet.  The  pellet  may  continue  to  fall  a  considerable  distance 
before  it  is  carried  up  again  by  a  strong  vertical  current  into  the  stratum  of 
supercooled  water  droplets  where  another  film  of  water  covers  it.  This  process 
may  be  repeated  many  times  until  the  pellet  can  no  longer  be  supported  by  the 
convective  updraft  and  falls  to  the  ground  as  hail.69 

(  Note:  The  lines  enclose  points  (stations)  that  have  equal  frequency  of  hail  days  ) 

Figure  7. — Average  annual  number  of  days  with  hail  at  a  point,  for  the  contiguous 
United  States.  (From  Changnon,  et  al.,  TASH,  1977.) 

68  National  Academy  of  Sciences,  "Climate  and  Food  ;  Climatic  Fluctuation  and  U.S. 
Agricultural  Production."  1976.  p.  141. 

89  Koeppe.  Clarence  E.  and  George  C.  de  Long,  "Weather  and  Climate,"  New  York,  Mc- 
Graw-Hill, 1958,  pp.  79-80. 


Modification  of  hail 

According  to  D.  Ray  Booker,  "Hail  modification  seeding  has  been 
done  operationally  for  decades  in  the  high  plains  of  the  United  States 
and  in  other  hail  prone  areas  of  the  world.  Thus,  there  appears  to  be  a 
significant  market  for  a  hail-reduction  technology."  70  In  the  United 
States  most  attempts  at  hail  suppression  are  conducted  by  commercial 
seeders  who  are  under  contract  to  State  and  county  governments  and  to 
community  associations.  There  are  also  extensive  hail  suppression  op- 
erations underway  in  foreign  countries.  Although  some  successes  are 
reported,  many  important  questions  are  still  unanswered  with  regard 
to  mitigation  of  hail  effects,  owing  largely  to  lack  of  a  satisfactory 
scheme  for  evaluation  of  results  from  these  projects. 

In  theory,  it  should  be  possible  to  inhibit  the  formation  of  large 
ice  particles  which  constitute  hailstones  by  seeding  in  order  to  increase 
the  number  of  freezing  nuclei  so  that  only  smaller  ice  particles  will 
develop.  This  would  then  leave  the  cloud  with  insufficient  precipita- 
tion water  to  allow  the  accretion  of  supercooled  droplets  and  the 
formation  of  hail  of  damaging  size.  This  simplistic  rationale,  how- 
ever, does  not  provide  insight  into  the  many  complications  with 
which  artificial  nail  suppression  is  fraught ;  nor  does  it  explain  the 
seemingly  capricious  responses  of  hailstorms  to  seeding  and  the  incon- 
sistent results  which  characterize  such  modification  attempts.  As  with 
all  convective  systems,  the  processes  involved  are  very  complex.  They 
are  controlled  by  the  speed  of  movement  of  the  air  parcels  and  precipi- 
tation particles,  leading  to  complicated  particle  growth,  evaporation, 
and  settling  processes.71  As  a  result,  according  to  Changnon,  the  con- 
clusions from  various  hail  suppression  programs  are  less  certain  than 
from  those  for  attempts  to  enhance  rain  from  convective  clouds,  and 
they  are  best  labeled  "contradictory."  72 

Changnon  identifies  two  basic  approaches  that  have  been  taken 
toward  hail  modification : 

»Most  common  has  been  the  intensive,  high  rates  of  seeding  of  the  potential 
storm  with  silver  iodide  in  an  attempt  to  transform  nearly  all  of  the  super- 
cooled water  into  ice  crystals,  or  to  "glaciate"  the  upper  portion  of  the  clouds. 
However,  if  only  part  of  the  supercooled  water  is  transformed  into  ice,  the 
storm  could  actually  be  worsened  since  growth  by  accretion  is  especially  rapid 
in  an  environment  composed  of  a  mixture  of  supercooled  drops  and  ice  crystals. 
Importantly,  to  be  successful,  this  frequently  used  approach  requires  massive 
seeding  well  in  advance  of  the  first  hailstone  formation. 

The  second  major  approach  has  been  used  in  the  Soviet  Union  and  *  *  *  in  the 
National  Hail  Research  Experiment  in  Colorado.  It  involves  massive  seeding 
with  silver  iodide,  but  only  in  the  zone  of  maximum  liquid  water  content  of  the 
cloud.  The  hope  is  to  create  many  hailstone  embryos  so  that  there  will  be  in- 
sufficient supercooled  water  available  to  enable  growth  to  damaging  stone  sizes." 

70  Booker,  D.  Ray,  "A  Marketing  Approach  to  Weather  Modification,"  background  paper 
prepared  for  the  U.S.  Department  of  Commerce  Weather  Modification  Advisory  Board. 
Feb.  20,  1977.  p.  4. 

i  National  Academy  of  Sciences,  "Climate  and  Food;  Climatic  Fluctuation  and  U.S. 
Agricultural  Production."  1070.  p.  143. 

72  Changnon,  "Present  and  Future  of  Weather  Modification ;  Regional  Issues,"  1975, 
p.  102. 

™ Ibid. 


Precipitation  instrument  site,  including,  from  left  to  right,  hailcube,  anemom- 
eter, rain/hail  separator,  and  Belfort  weighing  precipitation  gage.  (Courtesy  of 
the  National  Science  Foundation. ) 

Hail  seeding  technologies 

The  most  significant  field  programs  in  hail  suppression  during  recent 
years  have  included  those  conducted  in  the  Soviet  Union,  in  Alberta, 
in  South  Africa,  and  in  northeastern  Colorado  (the  National  Hail 
Research  Experiment).  In  the  course  of  each  of  these  projects,  some 
of  which  are  still  underway,  various  procedural  changes  have  been 
initiated.  In  all  of  them,  except  that  in  South  Africa,  the  suppression 
techniques  are  based  on  increasing  the  number  of  hail  embryos  by 


seeding  the  cloud  with  ice  nuclei.  Usually,  the  seeding  material  is 
silver  iodide,  but  the  Russians  also  use  lead  iodide,  and  on  occasion 
other  agents  such  as  sodium  chloride  and  copper  sulfate  have  been 
used.  The  essential  problems  in  seeding  for  hail  suppression  are  re- 
lated to  how,  when,  and  where  to  get  the  seeding  agent  into  potential 
hail  clouds  and  how  to  identify  such  clouds.74 

Soviet  suppression  techniques  are  based  on  their  hypothesis  that 
rapid  hail  growth  occurs  in  the  "accumulation  zone,"  just  above  the 
level  of  maximum  updraft,  where  liquid  water  content  can  be  as 
great  as  40  grams  per  cubic  meter.  To  get  significant  hail,  the  maximum 
updraft  should  exceed  10  to  15  meters  per  second,  and  the  temperature 
in  this  zone  must  be  between  0  and  —25°  C.  Upper  large  droplets 
freeze  and  grow,  combining  with  lower  large  droplets,  and  an  increase 
in  particle  size  from  0.1  cm  to  2  or  3  cm  can  occur  in  only  4  to  5  minutes. 
In  the  several  Russian  projects,  the  seeding  agent  is  introduced  at 
selected  cloud  heights  from  rockets  or  antiaircraft  shells ;  the  number 
of  volleys  required  and  the  position  of  injection  being  determined  by 
radar  echo  characteristics  and  past  experience  in  a  given  operational 

In  other  hail  suppression  projects,  seeding  is  most  frequently  carried 
out  with  aircraft,  from  which  flares  containing  the  seeding  agent  are 
released  by  ejection  or  dropping.  Each  flare  may  contain  up  to  100 
grams  of  silver  iodide ;  and  the  number  used  as  well  as  the  spacing  and 
height  of  ignition  are  determined  from  cloud  characteristics  as  well  as 
past  experience  in  a  given  experiment  or  operation.  In  each  case  it 
is  intended  to  inject  the  seeding  material  into  the  supercooled  portion 
of  the  cloud. 

Evaluation  of  hail  suppression  technology 

It  appears  that  mitigation  of  the  effects  of  hail  has  some  promise, 
based  on  the  collection  of  total  evidence  from  experiments  and  opera- 
tions around  the  world.  In  the  Soviet  Union,  scientists  have  been 
reporting  spectacular  success  (claims  of  60  to  80  percent  reduction)76 
in  hail  suppression  for  nearly  15  years;  however,  their  claims  are  not 
universally  accepted,  since  there  has  not  been  careful  evaluation  under 
controlled  conditions.  Hail-seeding  experiments  have  had  mixed  results 
in  other  parts  of  the  world,  although  a  number  of  commercial  seeders 
have  claimed  success  in  hail  damage  reduction,  but  not  with  convincing 

Successful  hail  suppression  reports  have  come  from  a  number  of 
operational  programs  in  the  United  States  as  well  as  from  weather 
modification  activities  in  the  Soviet  Union  and  in  South  Africa.  Often 
the  validity  of  these  results  is  questionable  in  view  of  deficiencies  in 
project  design  and  data  analysis;  nevertheless,  the  cumulative  evidence 
suggests  that  hail  suppression  is  feasible  under  certain  conditions. 
There  are  also  reports  of  negative  results,  for  example,  in  foreign  pro- 
grams and  in  the  National  Hail  Research  Experiment  in  the  United 

7*Chan*rnon.  Stanlev  A..  Jr..  and  Griffith  M.  Moroni.  Jr..  "Desipn  of  an  Experiment  To 
Suppress  Hail  In  Illinois."  Illinois  State  Water  Survey.  TSWS/R  01  /7fi.  RnHetln  01.  State  ot 
Illinois.  Department  of  Registration  and  Education,  Urbana,  1970.  pp.  82-S3. 

75  Ibid.,  p.  S3. 

70  Chancrnon.  "Present  and  Future  of  Weather  Modification,"  107".  p  102. 

77  Rattan.  Louis  J.  statement  submitted  to  Subcommittee  on  Environment  and  Atmos- 
phere Committee  on  Science  and  Technology,  U.S.  House  of  Representatives,  at  hearings. 
June  18,  1970,  pp.  7-8. 


States,  which  indicate  that  under  some  conditions  seeding  induces 
increased  hail.78 

Atlas  notes  that  this  apparent  dichotomy  has  until  recently  been 
attributed  to  different  approaches  to  the  techniques  and  rates  of  seed- 
ing. However,  lie  observes  that  both  positive  and  negative  results 
have  been  obtained  using  a  variety  of  seeding  methods,  including 
ground-  and  cloud-based  generators,  flares  dropped  from  above  the 
cloud  top,  and  injection  by  rockets  and  artillery.79  In  discussing  the 
reasons  for  increased  hail  upon  seeding,  Atlas  states : 

There  are  at  least  four  physical  mechanisms  by  which  seeding  may  produce 
increased  hail.  Two  of  these  occur  in  situations  in  which  the  rate  of  supply  of 
supercooled  water  exceeds  that  which  can  be  effectively  depleted  by  the  com- 
bination of  natural  and  artificially  produced  hail  embryos.  This  may  occur  in 
supercell  storms  and  in  any  cold-base  storm  in  which  the  embryos  are  graupel 
rather  than  frozen  raindrops.  Moreover,  present  seeding  methods  are  much  more 
effective  in  warm-base  situations  in  which  the  hail  embryos  are  frozen  raindrops. 
Increased  hail  is  also  probable  when  partial  glaciation  of  a  cloud  is  produced 
and  the  hail  can  grow  more  effectively  upon  the  ice-water  mixture  than  upon 
the  supercooled  water  alone.  Similarly,  increases  in  the  amount  of  hail  may 
occur  whenever  the  additional  latent  heat  resulting  from  nucleation  alters  the 
undraft  profile  in  such  a  manner  as  to  increase  its  maximum  velocity  or  to 
shift  the  peak  velocity  into  the  temperature  range  from  —20°  to  —30°  C,  where 
the  accreted  water  can  be  more  readily  frozen.  A  probable  associated  effect  is 
the  redistribution  of  precipitation  loading  by  the  combination  of  an  alternation 
in  the  updraft  velocity  and  the  particle  sizes  such  that  the  hail  embroyos  may 
grow  for  longer  durations  in  a  more  favorable  growth  environment.80 

Surreys  of  hail  suppression  effectiveness 

Recently,  Changnon  collected  information  on  the  effectiveness  of 
hail  suppression  technology  from  three  different  kinds  of  sources.  One 
set  of  data  was  based  on  the  results  of  the  evaluations  of  six  hail  sup- 
pression projects;  another  was  the  collection  of  the  findings  of  three 
published  assessments  of  hail  modification ;  and  the  third  was  obtained 
from  two  opinion  surveys  conducted  among  weather  modification 
scientists.81  The  principal  statistics  on  the  estimated  capabilities  for 
hail  suppression  from  each  of  these  groups  of  sources  are  summarized 
in  table  7.  Where  available,  the  estimated  change  in  rainfall  accom- 
panying the  hail  modification  estimates  are  also  included.  Such  rain- 
fall changes  might  have  been  sought  intentionally  as  part  of  a  hail  sup- 
pression activity  or  might  result  simply  as  a  byproduct  of  the  major 
thrust  in  reducing  hail.  In  the  table,  a  plus  sign* indicates  an  estimated 
percentage  increase  in  hail  and/or  rainfall  while  a  minus  sign  signifies 
a  percentage  decrease. 

The  six  evaluations  in  part  A  of  table  7  are  from  both  experimental 
and  operational  projects,  each  of  which  was  conducted  for  at  least  3 
years  in  a  single  locale  and  in  each  of  which  aircraft  seeding  tech- 
niques were  used.  Thus,  the  results  of  a  number  of  earlier  experiments, 
using  ground-based  seeding  generators,  were  not  considered  in  the 
estimations.  Furthermore,  change  in  hail  due  to  suppression  activities 
was  defined  on  the  basis  of  crop-loss  statistics  rather  than  on  the  basis 
of  frequency  of  hail  days,  since  Changnon  does  not  consider  the  latter, 

7S  Atlas.  David,  "The  Paradox  of  Hail  Suppression,"  Science,  vol.  195,  No.  4274,  Jan.  14. 
1977.  p.  195. 
79  Ibid. 

60  Ibid.,  pp  195-196. 

81  Chanjrnon.  Stanlev  A..  Jr..  "On  tbe  Status  of  Hail  Suppression."  Bulletin  of  the  Amer- 
ican Meteorological  Society,  vol.  58,  No.  1,  Jan.  1977,  pp.  20-28. 


along  with  other  criteria  such  as  number  and  size  of  hailstones,  hail 
mass,  and  radar  echo  characteristics,  to  be  a  reliable  indicator.82  Note 
that  five  of  the  six  projects  listed  indicate  a  hail  suppression  capability 
ranging  from  20  percent  to  48  percent.  Changnon  notes,  however,  that 
most  of  these  results  are  not  statistically  significant  at  the  5  percent 
level,  but  that  most  scientists  would  classify  the  results  as  "opti- 
mistic." 83 

Table  7— Status  of  Hail  Suppression  and  Related  Rainfall  Modification 
(Based  on  information  from  Changnon.  On  the  Status  of  Hail  Suppression. 


1.  Texas:  Hail  modification  was  —48  percent  (crop-loss  cost  value)  ;  no  change 
in  rainfall. 

2.  Southwestern  North  Dakota :  Hail  modification  was  —32  percent  (crop-hail 
insurance  rates)  ;  no  rain  change  information  available. 

3.  North  Dakota  pilot  project :  Hail  modification  was  —30  percent  (a  composite 
of  hail  characteristics,  radar,  and  crop-loss  data)  ;  change  in  rainfall  was  +23 

4.  South  Africa :  Hail  modification  was  —40  percent  (crop-loss  severity ; 
change  in  rainfall  was  —4  percent. 

5.  South  Dakota  "Statewide"  project :  Hail  modification  was  —20  percent 
(crop  loss)  ;  increase  in  rainfall  was  +?  percent. 

6.  National  hail  research  experiment  in  Colorado  : 

Increase  in  hail  mass  was  +4  percent  to  +23  percent,  with  median  of 
+23  percent : 
Increase  in  rainfall  was  +25  percent. 


1.  American  Meteorological  Society :  Positive  but  unsubstantiated  claims  and 
growing  optimism. 

2.  National  Academy  of  Sciences:  30  to  50  percent  reductions  in  U.S.S.R.  and 
15  percent  decreases  in  France — neither  result  proven  by  experimentation. 

3.  Colorado  State  University  Workshop : 

—30  percent  modification  nationwide ; 

—30  percent  modification  in  the  High  Plains,  with  ±  10-percent  change  in 
rain ;  unknown  results  in  the  Midwest ;  also  unknown  rainfall  effects. 


1.  Farhar-Grant  questionnaire  (214  answers)  :  —25  percent  crop-hail  damage 
nationwide,  although  majority — 59  percent — admit  they  do  not  know. 

2.  Illinois  State  Water  Survey  questionnaire  (63  answers)  : 

—30  percent  hail  loss,  with  +15  percent  rain  increasein  the  Great  Plains: 
—20  percent  hail  loss,  with  +10  percent  rain  increase  in  the  Midwest. 

The  results,  shown  in  part  B  of  table  7,  from  the  recent  published 
assessments  of  capability  in  hail  suppression  reveal  a  position  of 
"guarded  optimism;"  however,  there  is  no  indication  of  definitive 
proof  of  hail  suppression  contained  in  those  assessments.84  These  pub- 
lished assessments  are  comprised  of  a  statement,  on  the  status  of 
weather  modification  by  the  American  Meteorological  Society,85  the 
conclusions  of  a  study  on  the  progress  of  weather  modification  by  the 

82  Ibid.,  p.  22. 
*»Th1rt..  p.  26. 
"*  Ibid. 

"  American  Meteorological  Society.  "Policy  Statement  of  tbo  American  Meteorological 
Rocietv  on  Purposeful  and  Inadvertent  Modifier  Hon  of  Woatbcr  nnd  Climate,"  Bulletin  of 
tbo  American  Meteorological  Society,  vol.  ,r)4.  No.  7,  July  1073.  pp.  694-695. 


National  Academy  of  Sciences,86  and  a  report  on  a  workshop  at  Colo- 
rado State  University  on  weather  modification  and  'agriculture.87 

The  third  view  (part  C,  table  7)  resulting  from  two  opinion  surveys, 
indicates  wide-ranging  but  basically  "bipolar"  attitudes  among  the 
scientists  surveyed.  The  majority  of  the  experts  queried  felt  that  a  hail 
suppression  capability  could  not  be  identified;  however,  a  sizable 
minority  were  of  the  opinion  that  a  moderate  capability  for  modifying 
hail  (greater  than  20-percent  decrease)  does  now  exist.  Changnon  says 
that  the  results  of  these  opinion  surveys  show  at  best  that  the  con- 
sensus must  be  considered  to  be  a  pessimistic  view  of  a  hail  suppres- 
sion capability.88 

In  his  conclusions  on  the  status  of  hail  suppression  technology, 
Changnon  states : 

These  three  views  of  the  current  status  of  hail  suppression,  labeled  as  (1)  opti- 
mistic, (2)  slightly  optimistic,  and  (3)  pessimistic,  reflect  a  wide  range  of  opin- 
ion and  results.  Clearly,  the  present  status  of  hail  suppression  is  in  a  state  of 
uncertainty.  Reviews  of  the  existing  results  from  6  recent  operational  and  ex- 
perimental hail  suppression  projects  are  sufficiently  suggestive  of  a  hail  sup- 
pression capability  in  the  range  of  20  to  50  percent  to  suggest  the  need  for  an 
extensive  investigation  by  an  august  body  of  the  hail  suppression  capability 
exhibited  in  these  and  other  programs. 

One  of  the  necessary  steps  in  the  wise  experimentation  and  future  use  of  hail 
suppression  in  the  United  States  is  to  cast  the  current  status  in  a  proper  light. 
This  can  only  be  accomplished  by  a  vigorous  in-depth  study  and  evaluation  of 
the  results  of  the  recent  projects.88 

Conclusions  from  the  TASH  study 

Sponsored  by  the  Eesearch  Applied  to  National  Needs  program  of 
the  National  Science  Foundation,  a  major  technology  assessment  of 
hail  suppression  in  the  United  States  was  conducted  from  1975  through 
1977,  by  an  interdisciplinary  research  team.90  This  Technology  Assess- 
ment of  the  Suppression  of  Hail  (TASH)  study  was  intended  to  bring 
together  all  of  the  considerations  involved  in  the  application  of  hail 
suppression,  in  the  present  and  in  the  future,  to  ascertain  the  net  value 
of  such  technology  to  society.  The  goals  of  the  study  were : 

To  describe  the  current  knowledge  of  hail  suppression. 
To  identify  long-range  expectations  for  such  a  technology. 
To  estimate  the  societal  impacts  that  might  be  generated  by  its  wide  use. 
To  examine  public  policy  actions  that  would  most  equitably  direct  its  beneficial 

From  its  interdisciplinary  study  of  hail  suppression  and  its  impacts 
the  TASH  team  reached  the  following  broad  conclusions  on  the  effects 
of  hail  and  on  the  potential  technology  for  suppression  of  hail : 

The  United  States  experiences  about  $850  million  in  direct  crop  and  property 
hail  losses  each  year,  not  including  secondary  losses  from  hail.  The  key  character- 
istic of  hail  is  its  enormous  variability  in  size,  time,  and  space. 

Among  the  alternative  ways  of  dealing  with  the  hail  problem,  including  crop 
insurance,  hail  suppression,  given  a  high  level  of  development,  appears  to  be  the 
most  promising  future  approach  in  high  hail  loss  areas.  Economic  benefits  from 
effective  hail  suppression  vary  by  region  of  the  country,  with  the  most  benefit  to 

66  National  Academy  of  Sciences.  National  Research  Council.  Committee  on  Atmospheric 
Sciences.  "Weather  and  Climate  Modification  :  Problems  and  Progress,"  Washington,  D.C., 
1973.  pp.  100-106. 

87  Grant  and  Reid,  "Workshop  for  an  Assessment  of  the  Present  and  Potential  Role  of 
Weather  Modification  in  Agriculture  Production."  1975.  pp.  33-45. 

88  Changnon.  "On  the  Status  of  Hail  Suppression,"  1977,  p.  26. 
68  Ibid.,  pp.  26-27. 

90  Changnon.  et  al..  "Hail  Suppression  ;  Impacts  and  Issues."  Technology  Assessment  of 
the  Suppression  of  Hail  (TASH) ,  1977,  432  pp. 


be  derived  in  the  Great  Plains  area.  Any  alterations  in  rainfall  resulting  from 
hail  suppression  would  importantly  affect  its  economic  consequences. 

The  effects  of  cloud  seeding  on  rainfall  are  more  significant  than  its  effects  on 
hail  from  economic  and  societal  standpoints. 

At  the  present  time  there  is  no  established  hail  suppression  technology.  It  may 
be  possible  to  reduce  damaging  hail  about  25  percent  over  the  growing  season  in  a 
properly  conducted  project. 

Reducing  the  scientific  uncertainties  about  hail  suppression  will  require  a  sub- 
stantial commitment  by  the  Federal  Government  for  long-term  funding  of  a  sys- 
tematic, well-designed  program  of  research.  For  the  next  decade  or  so,  monitoring 
and  evaluation  of  operational  programs  will  be  important. 

Benefit-cost  analysis  revealed  that  investment  in  development  of  the  high-level 
technology  would  result  in  a  ratio  of  14 :1,  with  the  present  value  of  benefits  esti- 
mated to  total  $2.8  billion  for  20  years.  The  low-level  technology  showed  a  nega- 
tive benefit-cost  ratio.  Research  and  development  to  provide  the  high-level 
technology  is  the  best  choice  from  an  economic  standpoint;  a  minimal  level  of 
support  would  be  nonbeneficial.  In  a  word,  if  we  are  going  to  develop  hail  suppres- 
sion technology,  we  would  need  to  do  it  right. 

Effective  hail  suppression  will,  because  of  the  hail  hazard,  technological 
approach,  patterns  of  adoption,  and  institutional  arrangements,  lead  to  regionally 
coherent  programs  that  embrace  groups  of  States,  largely  in  the  Great  Plains. 

Some  would  gain  and  others  would  lose  from  widespread  application  of  an 
effective  hail  suppression  technology.  Farmers  within  adopting  regions  would 
receive  immediate  benefits  from  increased  production.  After  several  years  this 
economic  advantage  would  be  diminished  somewhat,  but  increased  stability  of 
income  would  remain.  Farmers  growing  the  same  crops  outside  the  adopting  areas 
would  have  no  advantages  and  would  be  economically  disadvantaged  by  commod- 
ity prices  lower  than  they  would  have  been  with  no  hail  suppression.  The  price 
depressing  effects  result  from  increased  production  in  adopting  areas.  Consumers 
would  benefit  from  slightly  decreased  food  prices.  The  impacts  generated  by  a 
highly  effective  technology  include  both  positive  and  negative  outcomes  for  vari- 
ous other  stake-holder  groups  in  the  Nation.  For  the  Nation  as  a  whole,  the 
impacts  would  be  minor  and  beneficial.  On  balance,  the  positive  impacts  outweigh 
the  negative  impacts  if  a  high-level  technology  can  be  developed. 

An  adequate  means  of  providing  equitable  compensation  on  an  economically 
sound  basis  for  persons  suffering  from  losses  due  to  cloud  seeding  has  not  been 
developed.  Some  better  procedure  for  compensating  losers  will  be  necessary.  In 
addition,  present  decision  mechanisms  and  institutional  arrangements  are  inade- 
quate to  implement  the  technology  in  a  socially  acceptable  manner.  Some  mecha- 
nism for  including  potential  opponents  in  the  decisionmaking  process  will  be 

It  is  unlikely  that  widespread  operational  hail  suppression  programs  would 
have  serious  adverse  environmental  impacts,  although  lack  of  sufficient  knowledge 
indicates  that  adverse  impacts  should  not  be  ruled  out.  Long-term  environmental 
effects  are  not  known  at  the  present  time.91 


Fog  poses  a  hazard  to  man's  transportation  activities,  particularly 
to  aviation,  where  as  a  result  of  delays  air  carriers  lose  over  $80  million 
annually.  Highway  accidents  attributed  to  fog  are  estimated  to  cost 
over  $300  million  per  year.92  Most  often  the  impetus  to  develop  effec- 
tive fog  and  stratus  cloud  dispersal  capabilities  has  come  from  the 
needs  of  commercial  and  military  aircraft  operations. 

There  are  two  basic  kinds  of  fog,  and  the  suppression  of  each  re- 
quires a  different  approach.  Supercooled  fog  and  stratus  clouds  are 
comprised  of  liquid  water  droplets  whose  temperature  is  below  f  reez- 

81  Farhar.  Barbara  C,  Stanley  A.  Changnon,  Jr.,  Earl  R.  Swanson,  Ray  J.  Davis,  and 
J  Eugene  Haas.  "Hail  Suppression  and  Societv.  Summary  of  Technology  Assessment  of  Hail 
Suppression,"  Urbana.  111..  "Illinois  State  Water  Survey,  June  1977."  pp.  21-22.  (This 
document  is  an  executive  summary  of  the  technology  assessment  by  Changnon,  et  al.,  "Hail 
Suppression  ;  Impacts  and  Issues.") 

92  National  Oceanic  and  Atmospheric  Administration,  "Summary  Report :  Weather  Modi- 
fication ;  Fiscal  Years  1969,  1970,  1971,"  Rockville,  Md.,  May  1973,  p.  72. 


ing  (i.e.,  0°  C  or  below).  Supercooled  fogs  account  for  only  about  5 
percent  of  all  fog  occurrences  in  the  United  States,  although  they  are 
prevalent  in  certain  parts  of  northeastern  and  northwestern  North 
America.  The  remainder  of  North  American  fogs  are  warm  fogs  (water 
droplets  warmer  than  0°  C).93  Although  cold  fog  has  been  amenable 
to  modification,  so  that  there  essentially  exists  an  operational  tech- 
nology for  its  dissipation,  practical  modification  of  warm  fogs,  on  an 
economical  basis,  has  not  yet  been  achieved. 

Cold  fog  modification 

Dispersal  of  cold  fog  by  airborne  or  ground-based  techniques  has 
been  generally  successful  and  has  become  an  operational  weather  modi- 
fication technology.  In  the  United  States  cold  fog  dispersal  operations 
have  been  conducted,  for  example,  by  commercial  airlines,  usually  with 
dry  ice  as  the  seeding  agent.  The  U.S.  Air  Force  has  also  operated 
ground-based  liquid  propane  systems,  at  domestic  and  foreign  bases, 
which  have  been  effective  in  dissipating  cold  fog  over  runways,  thus 
reducing  flight  delays  and  diversions.94  Conducted  largely  at  airports, 
cold  fog  suppression  is  usually  accomplished  using  aircraft,  which  drop 
various  freezing  agents,  such  as  dry  ice  or  silver  iodide  as  they  fly  over 
the  fog-covered  runways.  The  agents  initiate  ice  crystal  formation  and 
lead  to  precipitation  of  the  growing  crystals.95  Ground-based  systems 
for  cold  fog  dispersal  have  also  been  used  and  have  some  advantages 
over  airborne  systems.  Such  a  system  can  operate  continuously  for  ex- 
tended time  periods  more  economically  and  more  reliably. 

Warm  fog  modification 

The  remainder  of  North  American  fogs  are  "warm  fogs"  for  which 
a  suitable  dispersal  capability  remains  to  be  developed.  Crutchfield 
summarizes  the  status  of  warm  fog  dispersal  technology  and  its  eco- 
nomic potential : 

The  much  more  extensive  warm  fogs  which  cause  delays,  accidents,  and  costly 
interruptions  to  every  type  of  transportation  have  proved  intractable  to  weather 
modification  thus  far.  Some  success  has  been  achieved  on  occasion  by  heavy 
seeding  with  salt  and  other  materials,  but  results  have  not  been  uniformly  good, 
and  the  materials  used  have  presented  environmental  problems  in  the  areas 
treated.  Heating  airport  runways  has  been  of  some  benefit  in  dealing  with  warm 
fog,  but  at  present  is  not  generally  effective  in  cost-benefit  terms  and  can  inter- 
rupt air  traffic. 

Nevertheless,  the  research  and  technology  problems  involved  in  the  dispersal 
of  warm  fog  appear  to  be  of  manageable  proportions,  and  the  benefits  from  an 
environmentally  acceptable  and  predictable  technique  for  dealing  with  warm 
fog  would  be  of  very  real  interest  in  terms  of  economic  gain.96 

A  number  of  field  techniques  have  been  attempted,  with  some  meas- 
ure of  success,  for  artificial  modification  of  warm  fogs.  Seeding  is 
one  technique,  where  the  seeding  agents  are  usually  hygroscopic  parti- 
cles, solution  drops,  or  both.  There  are  two  possible  desired  effects  of 
seeding  warm  fogs,  one  being  the  evaporation  of  fog  droplets,  resulting 
in  visibility  improvement.  A  second  desired  effect  of  seeding,  results 
from  the  "coalescence"  process,  in  which  the  solution  droplets,  falling 

93  Changnon,  "Present  and  Future  of  Weather  Modification,"  1975,  p.  165. 

94  National  Oceanic  and  Atmospheric  Administration  "Summary  Report :  Weather  Modi- 
fication ;  Fiscal  Year  1973."  Rockville,  Md.,  December  1974,  pp.  39-40. 

9a  Changnon.  "Present  and  Future  of  Weather  Modification,"  1975.  p.  165. 

98  Crutchfield,  James  A.,  "Weather  Modification  :  The  Economic  Potential."  Paper  prepared 
for  U.S.  Department  of  Commerce  Weather  Modification  Advisory  Board.  University  of 
Washington,  Seattle,  May  1977,  pp.  5-6. 

34-857  O  -  79  -  9 


through  the  fog  layer,  collect  the  smaller  fog  droplets,  increasing 
visibility  as  the  fog  particles  are  removed  in  the  fallout.97  There  is  a 
wide  diversity  of  hygroscopic  particles  which  can  and  have  been  used 
for  warm  fog  dissipation.  Sodium  chloride  and  urea  are  the  most 
common,  but  others  have  included  polyelectrolyte  chemicals,  an  ex- 
ceedingly hygroscopic  solution  of  ammonium-nitrate  urea,  and  some 
biodegradable  chemicals.  Seeding  particle  size  is  critical  to  the  effec- 
tiveness of  a  warm  fog  dispersal  attempt ;  it  has  been  found  that  poly- 
dispersed  particles  (i.e.,  material  with  a  distribution  of  particle  sizes) 
are  more  effective  in  inducing  fog  modification  than  are  extra  fine 
particles  of  uniform  size,  which  were  only  thought  to  be  optimum  in 
earlier  experiments.  Other  problems  which  are  the  subject  of  con- 
tinuing study  relate  to  the  seeding  procedures,  including  the  number 
of  flights,  number  of  aircraft  to  be  used,  and  flight  patterns  in 
accordance  with  the  local  terrain  and  wind  conditions.  One  of  the 
most  difficult  operational  problems  in  the  seeding  of  warm  fog  is  that 
of  targeting.  One  solution  to  this  problem,  suggested  by  the  Air  Force, 
is  the  implementation  of  wide-area  seeding  instead  of  single-line 
seeding,  which  is  so  easily  influenced  by  turbulence  and  wind  shear.98 
Another  technique  for  dissipation  of  warm  fog  makes  use  of  heating. 
The  physical  principle  involved  is  the  vaporization  of  the  water  drop- 
lets through  introduction  of  sufficient  heat  to  vaporize  the  water  and 
also  warm  the  air  to  such  a  temperature  that  it  will  hold  the  additional 
moisture  and  prevent  condensation.  Knowing  the  amount  of  liquid 
water  in  the  atmosphere  from  physical  measurements,  the  necessary 
amount  of  heat  energy  to  be  injected  can  be  determined.99  The  fea- 
sibility of  this  approach  was  first  demonstrated  in  England  during 
World  War  II,  when  it  was  necessary  to  fly  aircraft  in  all  kinds  of 
weather  in  spite  of  frequent  fogbound  conditions  in  the  British  Isles. 
The  acronym  FIDO,  standing  for  Fog  Investigations  Dispersal  Of, 
was  applied  to  a  simple  system  whereby  fuel  oil  in  containers  placed 
along  the  runways  was  ignited  at  times  when  it  was  necessary  to  land 
a  plane  in  the  fog.  Although  burning  as  much  as  6,000  gallons  of  oil 
for  a  single  airplane  landing  was  expensive  and  inefficient,  it  was 
justified  as  a  necessary  weather  modification  technique  during  war- 

Initial  and  subsequent  attempts  to  disperse  fog  by  burning  liquid 
fuel  were  found  to  be  hazardous,  uneconomical,  and  sometimes  in- 
effective, and,  as  a  result,  not  much  was  done  with  this  heating  tech- 
nique until  the  French  revised  it,  developing  the  Turboclair  method 
for  dissipating  fog  by  heating  with  underground  jet  blowers.  After  10 
years  of  development  and  engineering  testing,  the  system  was  tested 
successfully  by  the  Paris  Airport  Authority  at  Orly  Airport.  This 
program  has  given  a  new  interest  and  stimulated  further  research  and 
development  of  this  technique  both  in  the  United  States  and  elsewhere. 
In  the  United  States,  the  Air  Force  conducted  Project  Warm  Fog 
to  test  the  effectiveness  of  heating  to  remove  warm  fog.  It  is  clear  that 
this  method  is  promising;  however,  further  studies  are  needed.1 

97  Mosohnndreas.  Demetrlos  J.,  "Present  Capabilities  to  Modify  Warm  Fog  and  Stratus," 
Geomet.  Inc..  report  No  EF-300.  Technical  report  for  Office  of  Naval  Research  and  Naval 
Air  Svstems  Command,  Rockvllle,  Md.,  Jan,  18,  1974,  p.  13. 

88  Ibid.,  pp.  16-17. 

"  Ibid    pp.  24.  30. 

Halacy,  Daniel  S.,  Jr.,  "The  Weather  Changers,"  New  York,  Harper  and  Row.  1968, 
pp.  105-107. 

1  Moschandreas.  "Present  Capabilities  to  Modify  Warm  Fog  and  Stratus,"  1974,  pp. 


Research  and  development  on  warm  fog  dispersal  systems  has  con- 
tinued under  sponsorship  of  the  U.S.  Air  Force,  using  both  passive 
heat  systems,  and  thermokinetic  systems  which  combine  both  heat  and 
mechanical  thrust.  A  thermokinetic  system,  known  as  the  Warm  Fog 
Dispersal  System  (WFDS),  consists  of  three  components:  The  com- 
bustors,  the  controls,  and  the  fuel  storage  and  distribution  hardware. 
Testing  of  the  WFDS  by  the  Air  Force  is  to  be  conducted  during  late 
1978  and  1979  at  Otis  Air  Force  Base  in  Massachusetts,  after  which  it 
is  to  be  installed  and  operational  at  an  Air  Force  base  by  1982.2  Dis- 
cussion of  the  Air  Force  development  program  and  of  the  concurrent 
studies  and  interest  on  the  Federal  Aviation  Administration  in  this 
thermokinetic  fog  dispersal  system  is  found  in  chapter  5  of  this  report.3 

There  have  been  attempts  to  evaporate  warm  fogs  through  mechani- 
cal mixing  of  the  fog  layer  with  warmer,  drier  air  from  above.  Such 
attempts  have  been  underway  using  the  strong  downwash  from  heli- 
copters ;  however,  such  a  technique  is  very  costly  and  would  likely  be 
employed  only  at  military  installations  where  a  number  of  helicopters 
might  be  available. 

The  helicopters  hover  or  move  slowly  in  the  dry  air  above  the  fog 
layer.  Clear  dry  air  is  moved  downward  into  the  fog  by  the  circulation 
of  the  helicopter  rotors.  The  mixture  of  dry  and  cloudy  air  permits  the 
fog  to  evaporate,  and  in  the  fog  layer  there  is  created  an  opening  whose 
size  and  lifetime  are  determined  by  the  meteorological  conditions  in 
the  area,  by  the  flight  pattern,  and  by  the  kind  of  helicopter. 

Conclusions  reached  by  scientists  involved  in  a  series  of  joint  U.S. 
Air  Force- Army  research  projects  using  helicopters  for  fog  dispersal 
follow : 

The  downwash  method  by  a  single  helicopter  can  clear  zones 
large  enough  for  helicopter  landing  if  the  depth  of  the  fog  is  less 
than  300  feet  (100  meters) . 

Single  or  multiple  helicopters  with  flight  patterns  properly 
orchestrated  can  maintain  continuous  clearings  appropriate  for 
aircraft  takeoff  and  landing  in  fogs  of  less  than  300  feet  (100 
meters)  deep.4 

In  addition  to  the  more  commonly  applied  experimental  techniques, 
such  as  seeding,  heating,  and  mechanical  mixing,  other  attempts  have 
been  made  to  disperse  warm  fogs.  These  have  included  the  injection  of 
ions  or  charged  drops  into  the  fog  and  the  use  of  a  laser  beam  to  clear 
the  fog.  Further  research  is  needed  before  definitive  results  can  be 
cited  using  these  methods.5 

Table  8  is  a  summary  of  research  projects  on  warm  fog  dispersal 
which  had  been  conducted  by  various  organizations  in  the  United 
States  between  1967  and  1973.  Note  that,  in  addition  to  field  experi- 
ments, research  included  modeling,  field  measurements  and  observa- 
tions of  fog,  chamber  tests,  statistical  interpretation,  model  evaluation, 
and  operational  assessment. 

On  the  basis  of  his  study  of  research  projects  through  1973  and 
claims  projected  by  the  scientists  involved  in  the  various  warm  fog 

8  Kunkel.  Bruce  A.,  "The  Design  of  a  Warm  Fog  Dispersal  System."  In  preprints  of  the 
Sixth  Conference  on  Planned  and  Inadvertent  Weather  Modification.  Champaign,  111.. 
Oct  10-13.  1977.  Boston,  American  Meteorological  Society,  1977,  pp.  174-176. 

3  See  pp.  305  and  308. 

4  Moschandreas,  "Present  Capabilities  To  Modify  Warm  Fog  and  Stratus,"  1974,  p.  45. 
6  Ibid.,  p.  14. 


modification  programs,  Demetrios  Moschandreas  formulated  the  fol- 
lowing conclusions  on  warm  fog  dispersal : 

Seeding  with  hygroscopic  particles  has  been  successful;  how- 
ever, targeting  problems  would  require  the  wide-area  approach  to 
seeding.  Urea  has  also  been  projected  as  the  agent  which  is  most 
effective  and  least  harmful  to  the  environment. 

The  heating  technique  is  very  promising  and  very  efficient; 
studies  for  further  verification  of  its  capabilities  are  in  order. 

The  helicopter  technique  by  itself  has  not  been  as  promising  as 
the  combination  of  its  use  with  hygroscopic  seeding. 

Studies  on  the  other  less  often  used  techniques  have  not  reached 
the  stage  of  wide  field  application. 

Numerical  modeling  has  provided  guidelines  to  the  field  experi- 
ments and  insights  to  the  theoretical  studies  of  fog  conditions. 

The  laboratory  experiments  have  given  the  scientists  the  con- 
trolled conditions  necessary  to  validate  a  number  of  theories.  The 
unique  contribution  of  chamber  tests  to  a  better  understanding  of 
the  dynamics  of  fog  formation  has  been  widely  recognized.6 


THROUGH  1973  « 

[From  Moschandreas,  1974] 

Area  of  effort 

Year  of  publication 

1967  2 







Modeling  and  numerical  ex- 





















Field  measurements;  fog  ob- 















Chamber  tests  






Field  experiments  












Statistical  interpretation 


Assessment  of  operational 







i  Research  is  listed  by  agency  conducting  the  research,  or  sponsoring  it,  when  reporting  its  contractor's  efforts;  or  by 
contractor's  name  when  contractor's  report  is  principal  reference;  individual  researchers  are  not  listed  because  these 
change,  even  though  the  cont;mjity  of  effort  is  maintained. 

s  Work  reported  prior  to  1967  is  not  included  here. 

Key:  CAL— Cornell  Aeronautical  Laboratory,  Inc.;  AFCRL— Air  Force  Cambridge  Research  Laboratories;  GEOMET— 
GEOMET,  Inc.;  MRI— Meteorology  Research,  Inc.;  NWRF— U.S.  Navy  Weather  Research  Facility;  EPRF— U.S.  Navy  En- 
vironmental Research  Facility;  EG&G— EG&G  Environmental  Services  Ooeration;  FAA— Federal  Aviation  Administra- 
tion: NCAR— National  Center  for  Atomospheric  Research;  NWC— Naval  Weapons  Center;  USNPGS— U.S.  Naval  Postgrad- 
uate School. 


At  any  given  time  over  the  whole  Earth  there  are  about  2,000  thun- 
derstorms in  progress,  and  within  these  storms  about  1,000  cloud-to- 
ground  discharges  are  produced  each  second.7  Lightning  is  essentially 
a  long  electric  spark,  believed  to  be  part  of  the  process  by  which  an 
electric  current  is  conducted  from  the  Earth  to  the  ipnosphere,  though 

-  1H1U.,   pp.   W^— »0.  I,  XT 

7  National  Science  Board.  "Patterns  and  Perspectives  In  Environmental  Science,  Na- 
tional Science  Foundation,  Washington,  D.C..  1972,  p.  157. 


the  origin  of  the  lightning  discharge  is  still  not  fully  understood.  In 
fair  weather  the  atmosphere  conducts  a  current  from  the  positively 
charged  ionosphere  to  the  ground,  which  has  a  negative  charge. 

The  details  of  the  charge-generating  process  within  a  thunderstorm 
are  not  well  understood,  though  theories  have  been  proposed  by  cloud 
physicists.  Probably  a  number  of  mechanisms  operate  together  to  bring 
about  cloud  electrification,  though,  essentially,  the  friction  of  the  air 
on  the  water  droplets  and  ice  crystals  in  the  storm  strips  off  electrons 
which  accumulate  near  the  base  of  cumulonimbus  clouds,  while  posi- 
tive charge  collects  in  the  upper  part.  The  negative  charge  near  the 
cloud  base  induces  a  local  positive  charge  on  the  Earth's  surface  be- 
neath, reversing  the  normal  fair  weather  situation.  When  the  electri- 
cal potential  between  the  cloud  and  ground  becomes  sufficiently  large, 
an  electrical  discharge  occurs,  in  which  electrons  flow  from  the  cloud 
to  the  ground.  In  addition,  there  are  discharges  between  clouds  and 
between  oppositely  charged  portions  of  the  same  cloud. 

In  the  rapid  sequence  of  events  which  comprise  a  lightning  stroke, 
the  initial,  almost  invisible,  flow  of  electrons  downward  from  cloud 
to  Earth,  called  the  leader,  is  met  by  an  upward-moving  current  of 
positive  charges,  establishing  a  conducting  path  of  charged  particles. 
A  return  stroke,  much  larger,  then  rushes  from  the  ground  to  the 
cloud.  All  of  these  events  appear  as  a  single  flash  since  they  occur  in 
about  fifty  microseconds;  however,  while  most  people  perceive  the 
lightning  stroke  as  travelling  from  cloud  to  ground,  it  is  actually  the 
return  stroke  which  provides  the  greatest  flash.8 

In  the  United  States,  lightning  kills  about  200  people  annually,  a 
larger  toll  than  that  caused  by  hurricanes.  Since  1940,  about  7,000 
Americans  have  lost  their  lives  from  lightning  and  related  fires.9  These 
casualties  occur  most  often  singly  or  occasionally  two  at  a  time,  so  that 
they  are  not  nearly  so  newsworthy  as  are  the  multiple  deaths  and 
dramatic  property  damage  associated  with  hurricanes,  tornadoes,  and 
floods.  On  the  other  hand,  a  lightning  problem  affecting  large  areas 
is  the  ignition  of  forest  fires,  some  10,000  of  which  are  reported  each 
year  in  the  United  States,  where  the  problem  is  most  acute  in  the 
Western  States  and  Alaska.10  Such  fires  inflict  damage  on  commercial 
timber,  watersheds,  scenic  beauty,  and  other  resources,  causing  an 
estimated  annual  damage  cost  of  $100  million.11  Other  examples  in 
which  lightning  can  be  especially  dangerous  and  damaging  include 
discharges  to  aircraft  and  spacecraft  and  effects  on  such  activities  as 
fuel  transfer  operations  and  the  handling  of  explosives. 

Because  of  the  relative  isolation  of  personal  accidents  due  to  light- 
ning, the  only  feasible  controls  over  loss  of  life  are  through  implemen- 
tation of  safety  measures  which  prevent  exposure  or  by  protection 
of  relatively  small  areas  and  structures  with  lightning  arresters.  For- 
ested areas,  however,  require  large  area  protection  from  lightning- 
caused  fires  in  order  to  promote  sound  forest  management.  It  is  hoped 

8Anthes.  Richard  A.,  Hans  A.  Panofsky,  John  C.  CaMr,  and  Albert  Rango,  "The  AtmosT 
phere,"  Columbus.  Ohio.  Charles  E.  Merrill.  1975,  p.  174. 

9  U.S.  Department  of  Commerce,  "Peak  Period  for  Lierhtniner  Nears  ;  NOAA  Lists  Safety 
Rules."  News  Release  NOAA  77-156.  Washington.  DC.  June  19.  1977,  p.  1. 

10  Fuquay.  Donald  M.,  "Lightning  Damage  and  Lightning  Modification  Caused  by  Cloud 
Seeding."  In  Wilmot  N.  Hess  (ed.),  "Weather  and  Climate  Modification,"  New  York,  John 
Wiley  &  Sons,  1974,  p.  605. 

"Ibid.,  p.  604. 


that  the  widespread  damage  to  forest  resources  resulting  from  the 
lightning-fire  problem  can  be  alleviated  through  use  of  weather  modi- 
fication techniques. 

Lightning  modification 

General  approaches  to  lightning  suppression  through  weather  mod- 
ification, which  have  been  contemplated  or  have  been  attempted,  in- 
clude : 

Dissipation  of  the  cloud  system  within  which  the  thunderstorm 
originates  or  reduction  of  the  convection  within  the  clouds  so  that 
vigorous  updrafts  and  downdrafts  are  suppressed. 

Reduction  of  the  number  of  cloud-to-ground  discharges,  es- 
pecially during  critical  fire  periods. 

Alteration  of  the  characteristics  of  discharges  which  favor 
forest  fuel  ignition. 

Use  of  other  weather  modification  techniques  to  produce  rains 
to  extinguish  fires  or  to  decrease  the  probability  of  ignition 
through  increase  of  ambient  relative  humidity  and  fuel  moisture. 
Lightning  is  associated  with  convective  clouds;  hence,  the  most 
direct  suppression  method  would  involve  elimination  of  the  clouds 
themselves  or  of  the  convection  within  them.  Removal  of  the  clouds 
would  require  changes  to  gross  properties  such  as  temperature  insta- 
bility and  moisture  content  of  the  air ;  thus,  such  modification  is  not 
technically,  energetically,  or  economically  feasible.  However,  it  might 
be  possible  to  reduce  somewhat  the  convection  within  the  clouds.12 

The  formation  of  convective  clouds  depends  on  the  upward  motion 
of  moist  air  caused  by  thermal  instability  and  the  subsequent  produc- 
tion of  water  through  cooling.  This  condensation  releases  more  heat, 
which,  in  turn,  causes  further  buoyancy  and  rising  of  the  cloud.  At 
these  heights  the  temperature  is  low  enough  that  the  water  can  freeze, 
releasing  more  latent  heat  and  enabling  the  cloud  particles  to  rise 
even  higher.  As  a  result  of  the  presence  of  nuclei  which  are  naturally 
present  in  the  cloud,  glaciation  proceeds  continuously.  Through  arti- 
ficial nucleation,  by  seeding,  natural  glaciation  may  be  reinforced  and 
development  of  the  cloud  assisted.  Rapid,  premature  seeding,  how- 
ever, would  still  promote  buoyancy  but  could  also  introduce  so  much 
turbulence  that  the  cloud  is  unable  to  develop,  because  colder  air  en- 
tering the  cloud  by  turbulent  mixing  would  lower  the  changes  of  the 
cloud  reaching  moderate  altitudes.  Since  there  is  a  high  correlation 
between  cloud  height,  convective  activity,  and  lightning,  such  early 
nucleation  of  a  cloud  should  reduce  the  likelihood  of  intense  elec- 
trical activity.  Seeding  would  be  accomplished  by  releasing  silver 
iodide  into  the  cores  of  growing  cumulus  clouds ;  it  could  be  delivered 
from  ground  dispensers  or  from  aircraft  into  the  updraft  under  the 
cloud  base.  The  amount  of  seeding  material  must  be  chosen  carefully, 
and,  in  order  to  increase  the  chances  for  cloud  dissipation,  overseed- 
ing  is  probably  most  effective,  though  such  overseeding  will  also  tend 
to  reduce  precipitation.  On  the  other  hand,  rainfall  may  be  advan- 
tageous for  other  purposes,  including  its  inhibiting  lightning-caused 
forest  fires  by  providing  moisture  to  the  forest  fuel.  Consequently,  the 
advantages  which  might  be  achieved  through  reducing  cloud  con- 

13  Stow,  C.  D..  "On  the  Prevention  of  Lightning,"  Bulletin  of  the  American  Meteorological 
Society,  vol.  50,  No.  7,  July  1969,  p.  515. 


vection  and  its  attendant  electrical  activity  must  be  weighed  against 
the  possible  advantages  lost  through  reduced  precipitation.13 

A  more  efficient  lightning-suppression  approach  might  involve  in- 
terference with  the  processes  which  bring  about  charge  separation  in 
the  cloud.  At  least  five  different  mechanisms  by  which  cloud  electrifica- 
tion is  established  have  been  theorized,  and  possibly  all  or  most  of  these 
mechanisms  are  active  in  any  given  situation,  although  on  different 
occasions  it  is  likely  that  some  are  more  effective  than  others,  depend- 
ing on  meteorological  conditions  and  geographical  locations.14  Data 
are  as  yet  insufficient  for  determining  which  mechanisms  will  predomi- 
nate. It  is  not  considered  likely  that  a  single  treatment  method  would 
suffice  to  suppress  all  lightning  activity  through  prevention  of  charge 
buildup,  though  it  is  conceivable  that  a  given  treatment  may  be  capable 
of  suppressing  more  than  one  charge-generating  process.15  In  addition 
to  glaciation  of  the  cloud  by  overseeding  (described  above  in  connec- 
tion with  convection  reduction),  accumulation  of  charge  can  be  in- 
hibited through  seeding  with  various  chemicals  which  affect  the 
freezing  of  water.  Another  technique  uses  seeding  with  a  conducting 
chaff  (very  fine  metalized  nylon  fibers),  which  increases  conductivity 
between  oppositely  charged  regions  of  the- storm  and  keeps  the  electric 
field  from  building  up  to  the  lightning-discharge  level.  The  chaff  fibers 
are  of  the  type  that  have  been  used  for  radar  "jamming,"  which  can  be 
dispensed  underneath  a  thunderstorm  from  an  aircraft.  Experiments 
have  shown  this  attempt  at  lightning  suppression  to  have  some 

Although  reduction  in  the  number  of  cloud-to-ground  discharges 
through  cloud  seeding  would  undoubtedly  be  instrumental  in  de- 
creasing the  total  number  of  forest  fires,  ignition  is  also  influenced  by 
such  factors  as  the  type  of  discharge,  surface  weather  conditions,  the 
terrain-fuel  complex,  and  the  influence  of  preceding  weather  on  fuel 
moisture.  The  kind  of  discharge  most  frequently  causing  forest  fires 
has  been  observed  and  its  characteristics  have  been  measured.  Observa- 
tions indicate  that  ignition  is  most  often  caused  by  hybrid  cloud-to- 
ground  discharges  having  long  continuing  current  phases,  whose 
duration  exceeds  40  milliseconds  and  that  the  probability  of  ignition  is 
proportional  to  the  duration  of  the  continuing  current  phase.17 

Evaluation  of  lightning  suppression  technology 

Seeding  experiments  to  date  have  yielded  results  which  suggest  that 
both  the  characteristics  and  the  frequency  of  lightning  discharges  have 
been  modified.  The  physical  processes  by  which  lightning  is  modified 
are  not  understood ;  however,  basic  physical  charging  processes  have 
been  altered  through  massive  overseeding  with  silver  iodide  freezing 
nuclei.  Direct  measurements  of  lightning  electricity  have  also  shown 
that  lightning  strokes  which  contain  a  long  continuing  current  are 
probably  responsible  for  most  lightning-ignited  forest  fires.  Keduction 
of  the  duration  of  the  long  continuing  current  discharge  through  wea- 
ther modification  techniques  may,  therefore,  be  more  significant  in 

13  Ibid. 

"  Ibid.,  pp.  516-519. 
16  Ibid  ,  p  519 

"  Kasemir.  Heinz  W..  "Lightning  Suppression  by  Chaff  Seeding  and  Triggered  Light- 
ning." In  Wilmot  N.  Hess  (editor),  "Weather  and  Climate  Modification,"  New  York,  Wiley. 
1974, N  pp.  612-622.  n       a  .     „     .  B   „ 

"Fuquav,  "Lightning  Damage  and  Lightning  Modification  Caused  by  Cloud  Seeding, 
1974,  p.  606. 


reducing  forest  fires  than  reduction  of  the  total  amount  of  lightning 
produced  by  storms. 

From  experiments  in  lightning  suppression  carried  out  under  Proj- 
ect Skyfire  by  the  U.S.  Forest  Service  of  the  Department  of  Agricul- 
ture between  1965-67.  Fuquay  summarizes  the  following  specific  re- 
sults, based  on  a  total  of  26  individual  storms  (12  seeded  and  14 
unseeded)  : 18 

Sixty-six  percent  fewer  cloud-to-ground  discharges,  50  percent 
fewer  intracloud  discharges,  and  54  percent  less  total  storm  light- 
ning occurred  during  seeded  storms  than  during  the  not-seeded 

The  maximum  cloud-to-ground  flash  rate  was  less  for  seeded 
storms :  over  a  5-minute  interval,  the  maximum  rate  averaged  8.8 
for  not-seeded  storms  and  5  for  seeded  storms;  for  15-minute  in- 
tervals, the  maximum  rate  for  not-seeded  storms  averaged  17.7 
and  9.1  for  seeded  storms. 

The  mean  duration  of  lightning  activity  for  the  not-seeded  and 
seeded  storms  was  101  and  64  minutes,  respectively.  Lightning 
duration  of  the  not-seeded  storms  ranged  from  10  to  217  minutes, 
while  that  of  seeded  storms  ranged  from  21  to  99  minutes. 

There  was  no  difference  in  the  average  number  of  return  strokes 
per  discrete  discharge  (4.1  not-seeded  versus  4  seeded)  ;  however, 
a  significant  difference  was  found  for  hybrid  discharges  (5.6  not- 
seeded  versus  3.8  seeded) . 

The  average  duration  of  discrete  discharges  (period  between 
first  and  last  return  stroke)  decreased  from  235  milliseconds  for 
not  seeded  storms  to  182  milliseconds  for  seeded  storms. 

The  average  duration  of  continuing  current  in  hybrid  dis- 
charges decreased  from  187  milliseconds  for  not-seeded  storms  to 
115  milliseconds  for  seeded  storms. 
In  a  recent  Federal  appraisal  of  weather  modification  technology 
it  was  concluded  that  results  of  field  experiments  to  suppress  light- 
ning through  silver  iodide  seeding  have  been  ambiguous.19  Although 
aim  lysis  of  data  previously  obtained  is  continuing,  the  experimental 
seeding  program  of  the  Forest  Service  has  been  terminated.  In  more 
recent  experiments,  thunderstorms  have  been  seeded  from  below 
with  chaff  (very  fine  metalized  nylon  fibers).  Based  on  an  analysis  of 
10  chaff-seeded  thunderstorms  and  18  unseeded  control  storms,  the 
number  of  lightning  occurrences  during  the  seeded  storms  was  about 
25  percent  of  those  observed  in  the  control  storms.  This  observed  differ- 
ence was  statistically  significant  even  though  the  experiments  were 
not  strictly  randomized.20 

Experiments  in  lightning  modification  through  cloud  seeding  have 
given  results  showing  that,  in  some  cases,  lightning  can  be  modified 
in  a  beneficial  manner.  From  these  results  and  the  measured  charac- 
teristics of  lightning  strokes,  a  hypothesis  of  lightning  modification  is 
being  developed.  There  has  been  progress  in  identifying  significant  cor- 
relations between  occurrence  of  lightning  and  such  variables  as  storm 

u  Fuquav.  "Lightning  Damage  and  Lightning  Modification  Caused  by  Cloud  Seeding," 
1974,  p.  6li. 

19  U.S.  Domestic  Council,  Environmental  Resources  Committee,  Subcommittee  on  Climate 
Change,  "The  Federal  Role  in  Weather  Modification."  Washington,  D.C.,  December  1975. 
p.  10. 



size,  updraft  characteristics,  precipitation  rates,  and  hail  occurrence. 
According  to  Fuquay,  such  early  successes  ought  not  obscure  the  mag- 
nitude of  the  research  yet  required  in  order  to  identify  and  quantify 
the  degree  and  applicability  of  lightning  modification  to  the  lightning- 
fire  problem.21  He  also  warns  that : 

Until  more  is  known  about  the  adverse  effects  of  seeding  incipient  thunder- 
storms, unexpected  and  adverse  effects  must  be  considered,  although  improved 
numerical  models  that  accurately  predict  cloud  development  and  the  effects  of 
seeding  should  minimize  the  risk  of  unexpected  events.22 


Severe  storms  have  a  greater  immediate  impact  on  human  life  and 
property  than  most  other  weather  phenomena.  A  major  portion  of 
losses  due  to  natural  disasters  results  from  two  of  the  most  destructive 
kinds  of  severe  storms — hurricanes  and  tornadoes.  During  an  average 
year  the  U.S.  mainland  is  threatened  by  8  tropical  slorms  and  experi- 
ences over  600  tornadoes.23  Among  the  results  of  the  annual  devastation 
from  these  storms  are  the  loss  of  hundreds  of  lives  and  the  accumula- 
tion of  hundreds  of  millions  of  dollars  in  property  damage. 

Perhaps  the  most  important  problems  to  be  attacked  in  weather 
modification  are  associated  with  the  abatement  of  severe  storms.  While 
rainfall  augmentation  promises  borderline  economic  value  at  best,  al- 
ternatives which  can  contribute  more  significantly  to  severe  water 
shortages  may  prove  more  suitable.  On  the  other  hand,  the  annual 
threat  of  tolls  in  damages  and  fatalities  from  hurricanes  and  tornadoes 
will  persist  year  after  year,  and  research  directed  toward  modification 
of  these  severe  phenomena  requires  continued  support.  There  have  been 
dramatic  attempts,  with  some  successes,  in  demonstrating  the  potential 
reduction  of  the  hazards  of  hurricanes ;  however,  almost  no  research 
has  been  directed  toward  tornado  suppression. 


A  hurricane  is  an  intense  cyclone  which  forms  over  tropical  seas, 
smaller  in  size  than  middle-latitude  cyclones,  but  much  larger  than  a 
tornado  or  a  thunderstorm.  With  an  average  size  of  500  miles  (800 
kilometers)  in  diameter,  the  hurricane  consists  of  a  doughnut-shaped 
ring  of  strong  winds  in  excess  of  64  knots  which  surrounds  an  area  of 
extremely  low  pressure  and  calm  at  the  storm's  center,  called  the  eye.2* 
The  generic  name  for  all  vortical  circulations  originating  over  tropi- 
cal waters  is  "tropical  cyclone."  When  fully  developed  with  sufficiently 
strong  winds,  such  storms  are  called  hurricanes  in  the  Atlantic  and  the 
eastern  Pacific  Oceans,  typhoons  in  the  northwest  Pacific,  baguios  in 
the  Philippines,  Bengal  cyclones  in  the  Indian  Ocean,  and  willy-willies 
near  Australia.  For  a  tropic  cyclone  whose  winds  are  in  the  range  of 
33  to  64  knots,  the  official  name' in  the  United  States  is  a  tropical  storm. 
The  hurricane  season  is  that  portion  of  the  year  having  a  relatively 

21  Fuquay,  "Lightning  Damage  and  Lightning  Modification  Caused  by  Cloud  Seeding," 
1974.  p.  612. 

22  Ibid.,  p.  606. 

23  Feieral  Coordinator  for  Meteorological  Services  and  Supporting  Research.  "Federal 
Plan  for  Meteorological  Services  and  Supporting  Resenrch  :  Fiscal  Year  1973."  U.S.  Depart- 
ment of  Commerce,  National  Oceanic  and  Atmospheric  Administration,  Washington,  D.C., 
January  1972.  p.  1. 

24Anthes,  Richard  A..  Hans  A.  Panofskv.  -Tohn  J.  Cahir.  and  Albert  Rango.  "The  Atmos- 
phere." Columbus,  Ohio,  Charles  E.  Merrill.  1975.  p.  150. 


high  incidence  of  hurricanes  and  usually  is  regarded  as  the  period 
between  June  and  November  in  the  Northern  Hemisphere.25 

Owing  to  their  duration,  which  exceeds  that  of  earthquakes,  and  to 
their  violence,  which  approaches  that  of  tornadoes,  hurricanes  are  the 
most  destructive  natural  phenomena.  Prior  to  Hurricane  Agnes  in 
1972,  whose  total  damage  exceeded  $3  billion,  the  annual  hurricane 
property  losses  in  the  United  States  amounted  to  about  $450  million, 
although  two  hurricanes  in  the  1960's,  Betsy  (1965)  and  Camille 
(1969),  each  caused  damage  exceeding  $1.4  billion.26  Improved  tech- 
niques in  hurricane  detection  and  warning  have  dramatically  reduced 
the  number  of  deaths  caused  by  hurricanes ;  however,  property  losses 
have  continued  to  grow,  as  a  result  of  increased  population  and  activi- 
ties in  vulnerable  coastal  areas,  with  the  attendant  concentration  of 
new  houses,  buildings,  and  other  facilities  of  higher  replacement  value. 
Figure  8  shows  the  simultaneous  increase  in  property  losses  and  de- 
crease in  deaths  due  to  hurricanes  in  the  United  States  in  the  20th 
century  through  1969. 

Devastation  and  fatalities  occur  essentially  from  three  phenomena 
associated  with  hurricanes :  the  force  of  the  winds  in  the  storm  itself, 
the  storm  surge  on  coastal  areas,  and  flooding  which  can  result  from 
excessive  and  widespread  rainfall  as  the  storm  moves  inland.  Since 
wind  force  varies  with  the  square  of  the  wind  speed,  a  50-mile-per-hour 
wind  exerts  four  times  as  much  force  as  a  25-mile-per-hour  wind.  Ac- 
cordingly, a  10-percent  reduction  in  maximum  windspeed  yields  a  de- 
crease in  wind  force  of  about  20  percent.27  Attempts  to  modify  hurri- 
cane winds  can  thus  be  expected  to  reduce  storm  damage  caused  by 
winds  in  approximate  proportion  to  the  corresponding  reduction  in 
wind  force. 

25  Federal  Coordinator  for  Meteorological  Services  and  Supporting  Research,  U.S.  Depart- 
ment of  Commerce,  National  Oceanic  and  Atmospheric  Administration,  "National  Hurricane 
Operations  Plan,"  FCM  77-  2.  Washington,  D.C.,  May  1977,  pp.  6-7. 

20  Gentry,  K.  Cecil,  "Hurricane  Modification."  In  Wilmot  N.  Hess  (ed.).  "Weather  and 
Climate  Modification,"  New  York,  John  Wiley  &  Sons,  1974,  p.  497. 

27  Ibid.,  p.  498. 


Figure  8. — Losses  in  the  United  States  from  hurricanes,  1915  through  1969,  in 
5-year  periods  (from  National  Oceanic  and  Atmospheric  Administration). 

_  As  a  hurricane  moves  across  the  coast  from  the  sea.  the  strong  winds 
pile  up  water  to  extreme  heights,  causing  storm  surges.  The  resulting 
onrushing  water  wreaks  damage  to  shoreline  and  coastal  structures. 
The  severity  of  the  storm  surge  is  increased  by  the  hurricane-generated 
wind  waves  which  are  superimposed  on  the  surge.  From  Hurricane 
Camille,  the  storm  surge  at  Pass  Christian,  Miss.,  was  24.6  feet,  higher 
than  any  previous  recorded  tide.  As  a  result,  135  people  were  killed, 
63,000  families  suffered  personal  losses,  and  Mississippi  alone  sustained 
$1  billion  in  damage.28  The  height  of  the  storm  surge  depends  both  on 

Anthes,  Panofsky,  Cahir,  and  Rango,  "The  Atmosphere,"  1975,  p.  159. 


the  windspeed  and  the  shape  and  slope  of  the  sea  bottom  offshore.  If 
there  is  a  sharp  dropoff  in  depth  not  far  off  the  beach,  the  rise  of  the 
sea  level  will  be  small,  for  example.  Nearshore  attempts  to  modify  a 
hurricane  could  lead  to  uncertain  results,  depending  upon  local  condi- 
tions. If  the  windspeed  is  reduced  without  moving  the  position  of 
maximum  winds  along  the  coast,  the  overall  effect  would  likely  be  a 
reduction  in  storm  surge.  However,  should  the  modification  activity 
result  in  developing  a  new  windspeed  maximum  at  a  different  location, 
the  surge  might  increase  or  decrease,  depending  on  bathymetry  and 
bottom  topography.29  Solutions  are  not  yet  clear,  and  the  storm  surge 
prediction  problem  is  being  studied  intensely  with  the  use  of  numerical 

Major  hurricane  damage  can  often  be  attributed  to  heavy  rains  and 
the  massive  and  sudden  flooding  which  can  result  as  the  storm  move's 
inland.  In  mountainous  regions  especially,  the  floods  from  such  rain- 
fall can  be  devastating  in  losses  to  both  life  and  property.  Such  flood- 
ing was  a  major  contributor  to  the  118  deaths  and  $3.5  billion  in  prop- 
erty destruction 30  which  resulted  in  June  1972  from  Hurricane  Agnes, 
which  set  the  record  of  achieving  the  greatest  damage  toll  of  all  U.S. 
hurricanes.  Ironically,  Agnes  caused  almost  no  major  damage  as  it 
went  ashore.  Hurricane  modification  activities  which  have  been  at- 
tempted or  are  contemplated  are  unfortunately  not  designed  to  reduce 
the  rains  significantly,  but  are  intended  rather  to  reduce  the  maxi- 
mum winds.31 

Generation  and  characteristics  of  hurricanes 

A  hurricane  can  be  thought  of  as  a  simple  heat  engine  driven  by 
temperature  differences  between  the  center  of  the  storm  and  its  mar- 
gins. At  each  level  the  central  column  must  be  warmer  than  the 
surrounding  area  to  insure  maintenance  of  the  strong  convection  on 
which  the  storm  depends.32  While  the  energy  which  forms  extratropical 
cyclones  is  provided  by  temperature  differences  between  different  air 
masses,  the  energy  which  generates  and  maintains  hurricanes  and 
other  tropical  cyclones  is  derived  from  a  single  air  mass  through 
condensation  of  water  vapor,  and  there  are  seldom  present  any  of 
the  frontal  activities  which  are  characteristic  of  storms  originating 
in  temperate  latitudes.  The  moisture-laden  winds  continuously  supply 
water  vapor  to  the  tropical  storm,  and  the  condensation  of  each  gram 
of  the  vapor  releases  about  580  calories  of  latent  heat.  Within  this 
thermally  driven  heat  engine  tremendous  quantities  of  energy  are 
converted  from  heat  to  mechanical  motion  in  a  short  time,  a  fact 
readily  apparent  from  the  fury  of  the  winds.  The  daily  power  of  the 
energy  liberated  within  a  hurricane  has  been  estimated  to  be  about 
ten  thousand  times  the  daily  power  consumption  in  the  United  States.33 
The  importance  of  tin1  ocean  in  providing  moisture  to  a  hurricane 
is  seen  in  the  weakening  and  dissipation  of  the  storms  after  they  have 
crossed  coastlines  and  travel  over  land. 

20  Gentrv.  "Hurricane  Modification,"  1974.  p.  499. 

30  National  Advisory  Committee  on  Oceans  and  Atmosphere.  "The  Agnes  Floods.:  a  Cost- 
Audit  of  the  Effectiveness  of  t^c  Storm  and  Flood  Warning  System  of  the  National  Oceanic 
and  Atmosnheric  Administration,"  a  report  for  the  Administrator  of  NOAA.  Washington, 
D.C.,  Nov.  22.  1972.  p.  1. 

:;1  Gentrv.  "Hurricane-Modification."  H>74.  n.  490. 

^Donn.  William  L.  "Meteorology."  4th  edition.  New  York.  McGraw-Hill,  1975,  p.  336. 
"Ibid.,  p.  338. 


Exactly  how  hurricanes  form  is  not  yet  fully  understood.  They 
are  all  generated  in  the  doldrums  (a  region  of  equatorial  calms), 
though  rarely  if  ever  within  latitudes  closer  than  5  degrees  from  the 
Equator,  over  water  whose  temperature  is  at  least  27°  C.  The  relatively 
high  surface  temperature  is  necessary  for  initiation  of  the  convection. 
Hurricanes  are  relatively  rare  features  even  of  the  tropics,  and  the 
exact  triggering  mechanism  is  not  yet  known.34  Their  origin  is  usually 
traced  to  a  low  pressure  disturbance  which  originates  on  the  equatorial 
side  of  the  trough  of  an  easterly  wave. 

Such  a  tropical  disturbance  moves  slowly  westward  and  slightly 
poleward  under  the  direction  of  the  tropical  east  winds.  If  conditions 
are  right,  this  cluster  of  thunderstorms  intensifies  as  it  reaches  the 
region  near  the  boundary  between  the  tropical  easterlies  and  the 
middle-latitude  westerlies,  at  about  25°  latitude.  It  may  then  follow 
a  path  which  reverses  toward  the  east  as  it  leaves  the  tropics.  The 
tracks  of  13  major  hurricanes  in  the  Northwest  Atlantic  Ocean  are 
shown  in  figure  9. 

The  development  of  the  intense  storm  which  might  result  from  the 
conditions  noted  above  is  described  in  the  following  way  by  Anthes 
et  al. : 

The  increased  inflow  toward  the  center  of  falling  pressure  produces  increased 
lifting  of  air,  so  that  the  thunderstorms  become  more  numerous  and  intense.  The 
feedback  cycle  is  now  established.  The  inflowing  air  fuels  more  intense  thunder- 
storm convection,  which  gradually  warms  and  moistens  the  environment.  The 
warmer  air  in  the  disturbance  weighs  less,  and  so  the  surface  pressure  continues 
to  fall.  The  farther  the  pressure  falls,  the  greater  the  inflow  and  the  stronger 
the  convection.  The  limit  to  this  process  would  occur  when  the  environment  is 
completely  saturated  by  cumulonimbus  clouds.  Further  condensation  heating 
would  not  result  in  additional  warming,  because  the  heat  released  would  exactly 
compensate  for  the  cooling  due  to  the  upward  expansion  of  the  rising  air.35 

34  Ibid. 

35  Anthes,  Panofsky,  Cahir,  and  Rango,  "The  Atmosphere,"  1975,  p.  154. 


Figure  9. — Tracks  of  thirteen  major  hurricanes  in  the  Xorth  Atlantic  from  1879 
through  1955  (from  U.S.  Naval  Oceanographic  Office,  Publication  No.  21, 
Sailing  Directions  for  the  West  Indies,  1958). 

As  the  storm  forms,  the  winds  begin  to  strengthen  about  the  center, 
increasing  especially  to  the  right  of  the  direction  in  which  the  center 
is  moving,  normally  on  the  poleward  side.  The  clouds  organize  them- 
selves into  a  system  and  dense  cirrus  move  forward  in  the  direction 
of  the  movement  of  the  center.  Suddenly,  the  pressure  falls  over  a 
small  area  and  hurricane  force  winds  form  a  tight  band  of  20  to  40 


miles  radius  around  the  center.  The  well-organized  clouds  show  a 
spiraling  structure,  and  the  storm  acquires  an  eye,  a  small  nearly 
circular  area,  coinciding  with  the  region  of  lowest  pressure.  The  winds 
in  the  eye  are  light  and  variable  and  the  clouds  are  scattered  or 
entirely  absent.36  As  the  storm  matures,  the  pressure  ceases  to  fall 
and  the  maximum  winds  do  not  increase  further.  Now  the  storm  ex- 
pands horizontally  and  large  amounts  of  air  are  drawn  in.  As  the 
storm  expands  to  a  radius  of  about  200  miles  or  more  it  becomes  less 
symmetrical.  Figure  10  is  a  vertical  cross-section  of  the  structure  of 
a  typical  mature  hurricane,  showing  the  direction  of  flow  and  cloud 

In  spite  of  the  great  damage  and  fatalities  caused  by  hurricanes, 
their  effects  are  not  completely  destructive.  In  many  areas  of  South- 
east Asia  and  the  west  coast  of  Mexico,  tropical  storms  are  depended 
upon  for  a  large  part  of  the  water  supply.  Throughout  the  Southern 
United  States,  hurricanes  have  also  provided  valuable  drought  relief.38 
-  Hurricane  and  other  tropical  cyclones  are  always  characterized  by 
high  wind  velocities  and  by  torrential  rains.  Wind  velocities  of  60  to 
70  knots  and  more  are  normal  for  such  storms.  The  air  rotates  rapidly, 
moving  spirally  toward  the  center.  Maximum  gusts  exceed  100  knots 
and  may  reach  200  knots,  although  such  high  speeds  are  unrecorded 
since  instruments  are  blown  away  or  made  inoperable  at  these  wind 

Figure  10. — Vertical  cross  section  through  a  hurricane,  showing  typical  cloud 
distribution  and  direction  of  flow,  as  functions  of  height  and  distance  from 
the  eye.  (From  Anthes,  Panofsky,  Cahir,  and  Rango,  1975.) 

Compared  with  extratropical  storms,  hurricanes  are  generally  small, 
circularly  shaped  zones  of  intense  low  pressure,  with  very  steep  pres- 
sure gradients  between  the  center  and  the  periphery.  The  pressure 
drop  between  the  eye  and  the  periphery  is  quite  large,  20  to  70  milli- 
bars being  typical.  The  winds  are  in  a  constant  circular  cyclonic 
motion  (counterclockwise  in  the  Northern  Hemisphere  and  clockwise 
in  the  Southern  Hemisphere)  ;  however,  the  center  of  the  storm  is  a 

36  pPtterssen.  Sverre.  "Introduction  to  Meteorology,"  second  edition,  New  York,  McGraw- 
Hill.  1958,  pp.  242-243. 

37  Anthes.  Panofsky.  Cahir.  and  Rango.  "The  Atmosphere,"  1975.  p.  157. 

ssReihl,  Herbert,  "Introduction  to  the  Atmosphere,"  New  York,  McGraw-Hill,  1965,  pp. 

39  Gentilli.  J..  "Tropical  Cyclones."  In  Rhodes  W.  Fairbridge  fed.).  "The  Encyclopedia 
of  Atmospheric  Sciences  and  Astrogeology."  Reinhold,  New  York,  1967,  p.  1028. 

*  Widely  scattered 
_  — —  shallow  cumulus 


Distance  from  hurricane  center  (km) 


calm  region  of  low  pressure,  called  the  eye.  which  is  about  10  miles 
across  on  the  average.  The  warm  dry  character  of  this  region  is  due 
to  subsiding  air,  which  is  necessary  for  existence  of  the  storm.  Around 
the  eye  is  the  wall,  consisting  of  cumulonimbus  clouds  and  the  at- 
tendant extreme  instability  and  rising  motion;  in  the  wall  area  adja- 
cent to  the  eye,  heavy  rains  fall.  Out  from  the  central  zone  altostratus 
and  nimbostratus  clouds  mix  to  form  a  layer  with  a  radius  as  great 
as  200  miles.  At  higher  altitudes  and  reaching  to  the  outer  regions 
of  the  storm  is  a  mixture  of  cirrus  and  cirrostratus  clouds.40 

In  a  mature  hurricane  a  state  of  relative  equilibrium  is  reached 
eventually,  with  a  particular  distribution  of  wind,  temperature,  and 
pressure.  Such  distributions  for  a  typical  hurricane  are  shown  sche- 
matically in  figure  11.  Note  that  the  greatest  pressure  change  and  the 
maximum  windspeeds  are  in  the  region  of  the  wall  clouds,  near  the 
center  of  the  storm.41 

Figtjbe  11.— Radial  profiles  of  temperature,  pressure,  and  windspeed  for  a  mature 
hurricane.  The  temperature  profile  applies  to  levels  of  3  to  14  kilometers; 
pressure  and  windspeed  profiles  apply  to  levels  near  the  surface.  (From 
Gentry,  1974. ) 

Modification  of  hurricanes 

Since  the  damage  inflicted  by  hurricanes  is  primarily  a  result  of  the 
high  windspeeds,  the  principal  goal  of  beneficial  hurricane  modifica- 

40  Jerome  Williams.  John  J.  Hipsinson.  and  John  D.  Rohrhoujjh.  "Sea  and  Air:  The 
Naval  Environment,"  Annapolis.  Md..  U.S.  Naval  Institute.  1968,  pp.  262-263. 

41  Gentry.  "Hurricane  Modification."  1974.  pp.  502-503. 


tion  is  the  reduction  of  the  severity  of  the  storm's  maximum  winds. 
The  winds  result  from  the  pressure  distribution,  which,  in  turn,  is 
dependent  on  the  temperature  distribution.  Thus,  hurricane  winds 
might  be  reduced  through  reduction  of  temperature  contrasts  between 
the  core  of  the  storm  and  the  region  outside. 

Gentry  notes  that  there  are  at  least  two  important  fundamentals  of 
hurricanes  which  have  been  established  through  recent  studies,  which 
suggest  possible  approaches  to  modification  of  the  severity  of  the 
storms : 42 

The  transfer  of  sensible  and  latent  heat  from  the  sea  surface  to  the 
air  inside  the  storm  is  necessary  if  the  hurricane  is  to  reach  or  retain 
even  moderate  intensity. 

The  energy  for  the  entire  synoptic-scale  hurricane  is  released  by 
moist  convection  in  highly  organized  convective-scale  circulations  lo- 
cated in  and  around  the  eye  of  the  storm  and  in  the  major  rain  bands. 
The  first  principle  accounts  for  the  fact  that  hurricanes  form  only 
over  warm  tropical  waters  and  begin  to  dissipate  after  moving  over 
land  or  cool  water,  since  neither  can  provide  sufficient  energy  flow  to 
the  atmosphere  to  maintain  the  intensity  of  the  storm.  The  second 
principle  explains  why  such  a  low  percentage  of  tropical  disturbances 
grow  to  hurricane  intensity.  Possible  field  experiments  for  beneficial 
modification  of  hurricanes  follow  from  these  principles.  On  the  basis 
of  the  first,  techniques  for  inhibiting  evaporation  might  be  employed 
to  reduce  energy  flux  from  the  sea  surface  to  the  atmosphere.  Based 
on  the  second  principle,  it  might  be  possible  to  affect  the  rate  of  release 
of  latent  heat  in  that  small  portion  of  the  total  storm  which  is  occupied 
by  the  active  convective-scale  motions  in  such  a  way  that  the  storm  is 
weakened  through  redistribution  of  heating.43 

Gentry  discusses  a  number  of  possible  mechanisms  which  have  been 
suggested  for  bringing  about  changes  to  the  temperature  field  in  a 
hurricane.44  Since  the  warm  core  development  is  strongly  influenced 
by  the  quantity  of  latent  heat  available  for  release  in  air  columns  ris- 
ing near  the  center  of  the  storm,  the  temperature  might  be  decreased 
through  reducing  the  water  vapor  in  these  columns,  the  water  vapor 
originating  through  evaporation  from  the  sea  surface  inside  the  region 
of  high  storm  winds.  It  has  been  suggested  that  a  film  spread  over  the 
ocean  would  thus  reduce  such  evaporation.  No  such  film  is  available, 
however,  which  could  serve  this  purpose  and  withstand  rupturing  and 
disintegration  by  the  winds  and  waves  of  the  storm.  Another  sugges- 
tion, tiiat  the  cooling  of  the  sea  surface  might  be  achieved  through 
dropping  cold  material  from  ships  or  aircraft,  is  impractical,  since 
such  great  expenditure  of  energy  is  required.  It  has  also  been  postu- 
lated that  the  radiation  mechanisms  near  the  top  of  the  hurricane  might 
be  modified  through  distribution  of  materials  of  various  radiation 
properties  at  selected  locations  in  the  clouds,  thus  inducing  changes  to 
the  temperatures  in  the  upper  part  of  the  storm.  This  latter  suggestion 
needs  further  evaluation  both  from  the  standpoint  of  its  practicality 
and  from  the  effect  such  a  change,  if  included,  would  theoretically  have 
on  storm  intensity. 

The  potential  schemes  for  hurricane  modification  which  seem  to  be 
practical  logistically  and  offer  some  hope  for  success  involve  attempts 

42  Ibid.,  1974.  p.  503. 
«  Ibid.,  p.  504. 
44  Ibid.,  p.  505. 

34-857  O  -  79  -  10 


to  modify  the  mechanism  by  which  the  convective  processes  in  the  eye- 
wall  and  the  rain  bands  distribute  heat  through  the  storm.  Since  water 
vapor  is  condensed  and  latent  heat  released  in  the  convective  clouds,  it 
should  be  possible  to  influence  the  heat  distribution  in  the  storm 
through  changing  the  pattern  of  these  clouds.45  Recent  success  in 
modifying  cumulus  clouds  promises  some  hope  of  success  in  hurricane 
modification  through  cloud  seeding.  By  modifying  the  clouds  in  a  hur- 
ricane, the  storm  itself  may  be  modified,  since  the  storm's  intensity  will 
be  affected  through  changing  the  interactions  between  the  convective 
(cloud)  scale  and  the  synoptic  (hurricane)  scales.46  Figure  12  shows 
how  the  properties  of  a  hurricane  might  be  redistributed  as  a  result 
of  changing  the  temperature  structure  through  seeding  the  cumulus 
cloud  structure  outside  the  wall.  The  solid  curves  in  the  figure  repre- 
sent distributions  of  temperature,  pressure,  and  windspeed  identical 
with  those  shown  in  figure  11  without  seeding;  the  dashed  curves  rep- 
resent these  properties  as  modified  through  seeding.47 

The  first  attempt  at  hurricane  modification  was  undertaken  by  sci- 
entists of  the  General  Electric  Co.,  on  a  hurricane  east  of  Jacksonville, 
Fla.,  on  October  13, 1947.  Clouds  outside  of  the  wall  were  seeded  with 
dry  ice  in  order  to  cause  freezing  of  supercooled  water,  so  that  the  ac- 
companying release  of  latent  heat  might  alter  the  storm  in  some  man- 
ner. Results  of  the  experiment  could  not  be  evaluated,  however,  owing 
to  the  lack  of  adequate  measuring  equipment  for  recording  cloud  char- 
acteristics. Furthermore,  the  penetration  of  the  wall  clouds  to  the  eye 
or  to  the  area  of  intense  convection  in  the  storm's  rain  bands  was  pre- 
vented by  failure  of  navigation  aids.  Based  on  information  acquired 
from  more  recent  seeding  experiments  and  increased  understanding  of 
hurricanes,  it  seems  doubtful  that  the  1947  seeding  could  have  been 

«  Ibid. 

"Ibid.,  p.  504. 
«Ibid.,  pp.  504-505. 
48  Ibid.,  pp.  505-506. 


Figure  12. — Radial  profiles  of  temperature,  pressure,  and  windspeed  for  a  mature 
hurricane  before  (solid  curves)  and  possible  changes  after  (dashed  curves) 
seeding.  (The  solid  curves  are  the  same  as  those  in  fig.  11.)  (From  Gentry, 

Hurricane  seeding  experiments  were  undertaken  by  the  Department 
of  Commerce  and  other  agencies  of  the  Federal  Government  in  1961, 
initiating  what  came  to  be  called  Project  Stormfury.  To  date  only  four 
hurricanes  have'  actually  been  seeded  under  this  project — all  of  them 
between  1961  and  1971 ;  however,  Stormfury  has  also  included  inves- 
tigation of  fundamental  properties  of  hurricanes  and  their  possible 
modification  through  computer  modeling  studies,  through  careful 
measurements  of  hurricane  properties  with  research  probes,  and 
through  improvements  in  seeding  capabilities. 

The  goal  of  hurricane  seeding  is  the  reduction  of  the  maximum  winds 
through  dispersing  the  energy  normally  concentrated  in  the  relatively 
small  band  around  the  center  of  the  storm.  The  basic  rationale  for  seed- 
ing a  hurricane  with  silver  iodide  is  to  release  latent  heat  through 
seeding  the  clouds  in  the  eye  wall,  thus  attempting  to  change  the  tem- 
perature distribution  and  consequently  weaken  the  sea  level  pressure 
gradient.  It  is  assumed  that  the  weakened  pressure  gradient  will  allow 
outward  expansion,  with  the  result  that  the  belt  of  maximum  winds 
will  migrate  away  from  the  center  of  the  storm  and  will  therefore 
weaken.  Actually,  stimulation  of  condensation  releases  much  more 
latent  heat  than 'first  hypothesized  in  1961,  and  theoretical  hurricane 
models  show  that  a  new  eve  wall  of  greater  diameter  can  be  developed 
by  encouraging  growth  of  cumulus  clouds  through  dynamic  seeding.49 

»  Ibid.,  pp.  510-511. 


Following  seeding  of  the  four  storms  in  Project  Stormf ury,  changes 
were  perceived,  but  all  such  changes  fell  within  the  range  of  natural 
variability  expected  of  hurricanes.  In  no  case,  however,  did  a  seeded 
storm  appear  to  increase  in  strength.  Hurricane  Debbie,  seeded  first 
on  August  18,  1969,  exhibited  changes,  however,  which  are  rarely 
observed  in  unseeded  storms.  Maximum  winds  decreased  by  about  30 
percent,  and  radar  showed  that  the  eye  wall  had  expanded  to  a  larger 
diameter  shortly  after  seeding.  After  Debbie  had  regained  her  strength 
on  August  19,  she  was  seeded  again  on  August  20,  following  which 
her  maximum  winds  decreased  by  about  15  percent.50  Unfortunately, 
data  are  not  adequate  to  determine  conclusively  that  changes  induced 
in  Debbie  resulted  from  seeding  or  from  natural  forces.  Observations 
from  Hurricane  Debbie  are  partially  supported  by  results  from  simu- 
lated experiments  with  a  theoretical  hurricane  model ;  however,  simu- 
lation of  modification  experiments  with  other  theoretical  models  have 
yielded  contrary  results.51 

One  of  the  problems  in  evaluating  the  results  of  hurricane  modifi- 
cation is  related  to  the  low  frequency  of  occurrence  of  hurricanes 
suitable  for  seeding  experiments  and  the  consequent  small  number  of 
such  experiments  upon  which  conclusions  can  be  based.  This  fact  re- 
quires that  hurricane  seeding  experiments  must  be  even  more  carefully 
planned,  and  monitoring  measurements  must  be  very  comprehensive, 
so  that  data  acquired  in  the  few  relatively  large  and  expensive  experi- 
ments can  be  put  to  maximum  use.  Meanwhile  theoretical  models  must 
be  improved  in  order  to  show  the  sensitivity  of  hurricane  characteris- 
tics to  changes  which  might  be  induced  through  seeding  experiments. 

Gentry  has  suggested  that  the  following  future  activities  should  be 
conducted  under  Stormf  ury  : 52 

1.  Increased  efforts  to  improve  theoretical  models. 

2.  Collection  of  data  to  further  identify  natural  variability  in 

3.  Expanded  research — both  theoretical  and  experimental — on 
physics  of  hurricane  clouds  and  interactions  between  the  cloud 
and  hurricane  scales  of  motion. 

4.  More  field  experiments  on  tropical  cyclones  at  every  oppor- 

5.  Tests  of  other  methods  and  material  for  seeding. 

6.  Further  evaluation  of  other  hypotheses  for  modifying 

7.  Development  of  the  best  procedures  to  maximize  results  of 
field  experiments. 


The  structure  of  tornadoes  is  similar  to  that  of  hurricanes,  consist- 
ing of  strong  cyclonic  winds  53  blowing  around  a  very  low  pressure 
center.  The  size  of  a  tornado,  however,  is  much  smaller  than  that  of  a 
hurricane,  and  its  wind  force  is  often  greater.  The  diameter  of  a  tor- 
so National  Oceanic  and  Atmospheric  Administration.  "Stormfury— 1977  to  Seed  One 
Atlantic  Hurricane  U.S.  Department  of  Commerce  News,  NOAA  77-248,  Washington. 
D.C.,  Sept.  20.  1977,  p.  3. 

51  Gentry,  "Hurricane  Modification,"  1974.  p.  517. 

^  Cyclonic > winds  blow  counterclockwise  around  a  low  pressure  center  in  the  Northern 
Hemisphere  ;  in  the  Southern  Hemisphere  they  blow  clockwise. 


nado  is  about  one- fourth  of  a  kilometer,  and  its  maximum  winds  can 
exceed  250  knots  in  extreme  cases.54  On  a  local  scale,  the  tornado  is  the 
most  destructive  of  all  atmospheric  phenomena.  They  are  extremely 
variable,  and  their  short  lifetime  and  small  size  make  them  nearly 
impossible  to  forecast  with  any  precision. 

Tornadoes  occur  in  various  parts  of  the  world;  however,  in  the 
United  States  both  the  greatest  number  and  the  most  severe  tornadoes 
are  produced.  In  1976.  there  were  reported  832  tornadoes  in  this  coun- 
try,55 where  their  origin  can  be  traced  to  severe  thunderstorms,  formed 
when  warm,  moisture-laden  air  sweeping  in  from  the  Gulf  of  Mexico 
or  the  eastern  Pacific  strikes  cooler  air  fronts  over  the  land.  Some  of 
these  thunderstorms  are  characterised  by  the  Auolent  updrafts  and 
strong  tangential  winds  which  spawn  tornadoes,  although  the  details 
of  tornado  generation  are  still  not  fully  understood.  Tornadoes  are 
most  prevalent  in  the  spring  and  occur  over  much  of  the  Eastern  two- 
thirds  of  the  United  States;  the  highest  frequency  and  greatest  devas- 
tation are  experienced  in  the  States  of  the  middle  South  and  middle 
West.  Figure  13  shows  the  distribution  of  71,206  tornadoes  which 
touched  the  ground  in  the  contiguous  United  States  over  a  40-year 

Even  in  regions  of  the  world  favorable  to  severe  thunderstorms,  the 
vast  majority  of  such  storms  do  not  spawn  tornadoes.  Further- 
more, relatively  few  tornadoes  are  actually  responsible  for  deaths  and 
severe  property  damage.  Between  1960  and  1970,  85  percent  of  tornado 
fatalities  were  caused  by  only  1  to  iy2  percent  of  reported  tornadoes.56 
Nevertheless,  during  the  past  20  years  an  average  of  113  persons  have 
been  killed  annually  by  tornadoes  in  the  United  States,  and  the  annual 
property  damage  from  these  storms  has  been  about  $75  million.57 

Modification  of  tornadoes 

Alleviation  from  the  devastations  caused  by  tornadoes  through 
weather  modification  techniques  has  been  a  matter  of  considerable 
interest.  As  with  hurricanes,  any  such  modification  must  be  through 
some  kind  of  triggering  mechanism,  since  the  amount  of  energy  pres- 
ent in  the  thunderstorms  which  generate  tornadoes  is  quite  large.  The 
rate  of  energy  production  in  a  severe  thunderstorm  is  roughly  equal  to 
the  total  power-generating  capacity  in  the  United  States  in  1970.58 
The  triggering  mechanism  must  be  directed  at  modifying  the  circula- 
tion through  injection  of  small  quantities  of  energy. 

^  Anthes,  Panofsky,  Cahir,  and  Rango,  "The  Atmosphere,"  pp.  150,  180. 

50  NOAA  news.  "Skywarn  1977 — Defense  Against  Tornadoes,"  U.S.  Department  of  Com- 
merce, National  Oceanic  and  Atmospheric  Administration.  Rockville,  Md.,  Feb.  18,  1977, 
vol.  2,  No.  4,  pp.  4-5. 

56  Davies-Jones,  Robert  and  Edwin  Kessler,  "Tornadoes."  In  Wilmot  N.  Hess  (ed.), 
"Weather  and  Climate  Modification,"  New  York,  John  Wiley  &  Sons,  1974,  p.  552. 
»  Ibid. 

58  Anthes,  Panofsky,  Cahir,  and  Rango,  "The  Atmosphere,"  1975,  p.  185. 


Figure  13. — Tornado  distribution  in  the  United  States,  where  contours  enclose 
areas  receiving  equal  numbers  of  tornadoes  over  a  40-year  period.  Frequencies 
are  based  on  number  of  2-degree  squares  experiencing  first  point  of  contact 
with  the  ground  for  71,206  tornadoes.  (From  Wilkins,  1967,  in  Encyclopedia 
of  Atmospheric  Sciences  and  Astrology,  Reinhold.) 

Tornado  modification  has  not  been  attempted  in  view  of  the  pres- 
ent insufficient  knowledge  about  their  nature  and  the  lack  of  adequate 
data  on  associated  windspeeds.  There  are  potential  possibilities,  how- 
ever, which  can  be  considered  for  future  research  in  tornado  modifica- 
tion. One  proposal  is  to  trigger  competing  meteorological  events  at 
strategic  locations  in  order  to  deprive  a  tornadic  storm  of  needed  in- 
flow. This  technique,  suggested  by  the  presence  of  cumulus  clouds  over 
forest  fires,  volcanoes,  and  atomic  bomb  blasts  could  use  arrays  of 
large  jet  engines  or  oil  burning  devices.  Another  approach  for  dis- 
persal of  convective  clouds  which  give  rise  to  thunderstorms  might 
involve  the  use  of  downrush  created  by  flying  jet  aircraft  through 
the  clouds.  A  further  possibility  would  depend  on  changing  the  char- 
acteristics of  the  Earth's  surface  such  as  the  albedo  or  the  availability 
of  water  for  evaporation.59 

Tornadoes  tend  to  weaken  over  rougher  surfaces  due  to  reduction 
of  net  low-level  inflow.  Upon  meeting  a  cliff,  tornadoes  and  water- 
spouts often  retreat  into  the  clouds,  and  buildings  also  tend  to  reduce 
ground  level  damage.  Thus,  forests  or  artificial  mounds  or  ridges 
might  offer  some  protection  from  tornadoes,  although  very  severe 
tornadoes  have  even  left  swaths  of  uprooted  trees  behind.60 

Modification  of  tornadoes  by  cloud  seeding  would  likely  bo  the  cheap- 
est and  easiest  method.  Sodium  iodide  seeding  could  possibly  shorten 
the  life  of  a  tornado  if  the  storm's  cold  air  outflow  became  stronger  and 
overtook  the  vortex  sooner,  thus  cutting  off  the  inflow.  Seeding  a 
neighboring  cell  upstream  of  the  low-level  inflow  might  also  be  bene - 

09  Davies-Jones  and  Kessler,  "Tornadoes,"  1974,  p.  590. 
»  Ibid. 


ficial,  if  the  rapidly  developing  seeded  cloud,  competing  for  warm, 
moist  air,  reduces  the  inflow  and  weakens  the  rotating  updraft.  It  is 
also  possible  that  seeding  would  increase  low-level  convergence,  lead- 
ing to  intensification  of  a  tornado.61 
Davies- Jones  and  Kessler  conclude  that : 

Any  efforts  to  modify  a  severe  storm  with  potential  or  actual  tornadoes 
obviously  will  have  to  be  carried  out  with  extreme  caution  *  *  *.  Actual  modifica- 
tion attempts  on  menacing  tornadoes  are  probably  several  years  away.  In  the 
meantime,  we  should  seek  improved  building  codes  and  construction  practices 
and  continue  research  into  the  actual  morphology  of  convective  vortices.62 

In  spite  of  the  speculations  on  how  tornadoes  might  be  modified,  no 
tests  have  yet  been  conducted.  The  small  size  and  brief  lifetime  of  tor- 
nadoes make  them  difficult  and  expensive  to  investigate.  However,  in 
view  of  their  destructiveness,  they  must  be  given  more  attention  by 
meteorologists,  who  should  seek  ways  to  mitigate  their  effects.  Only 
further  research  into  the  character  of  tornadoes,  followed  by  careful 
investigation  of  means  of  suppressing  them,  can  lead  to  this  desired 
reduction  in  the  effects  of  tornadoes. 

Technical  Problem  Areas  in  Planned  Weather  Modification 

In  this  section  a  number  of  major  problem  areas  associated  with  the 
development  of  weather  modification  technology  will  be  addressed. 
These  topics  are  not  necessarily  confined  to  the  modification  of  any  one 
of  the  weather  phenomena  discussed  in  the  previous  section  but  apply 
in  general  to  a  number  of  these  categories  of  phenomena.  Some  of  the 
problem  areas  have  implications  which  extend  beyond  the  purely 
technical  aspects  of  planned  weather  modification,  bearing  also  on 
social,  economic,  and  legal  aspects  as  well.  Included  are  discussions  on 
the  problems  of  seeding  technology,  evaluation  of  results  of  weather 
modification  projects,  extended  area  and  extended  time  effects  from 
advertent  weather  modification,  and  potential  approaches  to  weather 
and  climate  modification  which  involve  techniques  other  than  seeding. 
The  problems  of  inadvertent  weather  modification  and  of  potential 
ecological  effects  from  planned  weather  modification  could  also  prop- 
erly be  included  in  this  section ;  however,  these  topics  are  addressed  in 
chapter  4  and  13,  respectively,  in  view  of  their  special  significance. 

seeding  techonology 

In  recent  years  there  has  been  progress  in  developing  a  variety  of 
ice-nucleating  agents  available  for  cloud  seeding,  although  silver  iodide 
continues  to  be  the  principal  material  used.  Other  seeding  agents  which 
have  been  studied  include  lead  iodide,  metaldehyde,  urea,  and  copper 
sulfide.  Nucleants  have  been  dispensed  into  the  clouds  from  both 
ground-based  generators  or  from  aircraft.  In  some  foreign  countries, 
such  as  the  Soviet.  Union,  rockets  or  artillery  have  been  used  to  place 
the  seeding  material  into  selected  regions  of  the  clouds;  however,  this 
means  of  delivery  does  not  seem  to  be  acceptable  in  the  United  States. 

There  have  been  both  difficulties  and  conflicting  claims  regarding  the 
targeting  of  seeding  materials,  particularly  from  groimd  generators, 
ever  since  the  earliest  days  of  cloud  seeding.  It  is  always  hoped  that 

ft  Ibid.,  pp.  590-591. 
«a  Ibid.,  p.  591. 


the  nucleant  will  be  transported  from  the  generator  site  by  advection, 
convection,  and  diffusion  to  parts  of  the  clouds  which  have  been  iden- 
tified for  modification.  Difficulties  have  been  observed  under  unstable 
conditions,  where  the  plume  of  nucleants  was  disrupted  and  wide  angle 
turbulent  diffusion  was  severe.  Valley  locations  in  mountainous  areas 
are  often  subjected  also  to  inversions  and  to  local  channeling  so  that 
trajectory  determinations  are  extremely  difficult.  Even  plumes  of  seed- 
ing material  from  aircraft  have  shown  an  erratic  pattern.  The  prob- 
lems of  irregular  plume  goemetry  appear  to  increase  as  distortion 
occurs  near  fronts  in  mountain  terrain,  that  is,  under  just  the  circum- 
stances where  cloud  seeding  is  often  attempted.63 

In  view  of  the  limited  vertical  transport  of  silver  iodide  observed 
in  some  studies  (that  is,  up  to  450  meters  above  the  terrain  at  distances 
of  several  kilometers  from  the  generators),  some  have  concluded 
that,  under  conditions  of  the  tests,  ground-based  generators  are 
probably  not  effective.  However,  other  studies  have  shown  that  one 
cannot  generalize  that  ground  generators  are  not  always  effective. 
Thus,  more  desirable  effects  can  be  achieved  with  generators  at  high 
altitudes  where  there  is  little  chance  of  inversion  trapping  of  the 
silver  iodide  as  in  other  tests.64 

Much  of  the  ambiguity  associated  with  ground-based  generators  is 
reduced  when  the  nucleant  material  is  placed  into  the  cloud  directly 
by  an  aircraft  using  flares  or  rockets.  However,  airborne  seeding  also 
presents  important  targeting  problems.  Of  course,  targeting  difficul- 
ties are  reduced  in  the  case  of  single  cloud  seeding,  where  the  aircraft 
is  flying  directly  beneath  the  cloud  in  the  active  updraft  area.  How- 
ever, questions  of  proper  vortical  ascent  persist  when  the  objective  is 
to  lay  down  from  the  aircraft  an  elevated  layer  of  nucleant-rich  air 
that  is  intended  to  drift  over  the  target  area.65 

In  conclusion,  the  1973  National  Academy  of  Sciences  study  says : 

To  summarize  the  results  of  the  past  few  years'  work  on  targeting,  it  can  he  said 
that  earlier  dobuts  about  the  inevitability  of  nuclei  reaching  effective  altitudes 
from  ground  generators  tend  to  be  supported  by  a  number  of  recent  observational 
studies.  Some  of  these  merely  confirm  the  rather  obvious  prediction  that  stable 
lapse  rates  will  be  unfavorable  to  the  efficacy  of  ground  generators ;  others  indi- 
cate surprising  lack  of  vertical  ascent  under  conditions  that  one  might  have 
expected  to  favor  substantial  vertical  transport.  The  recent  work  also  tends  to 
support  the  view  that  plumes  from  ground  generators  in  mountainous  terrain 
must  be  expected  to  exhibit  exceedingly  complex  behavior ;  and  each  site  must 
be  expected  to  have  its  own  peculiarities  with  respect  to  plume  transport.  Tracking 
experiments  become  an  almost  indispensable  feature  of  seeding  trials  or  operations 
in  such  cases.66 

There  are  three  types  of  airborne  seeding  agent  delivery  systems  in 
common  use — burners,  flares,  and  hoppers.  Burners  are  used  mainly 
for  horizontal  seeding,  often  at  the  cloud  base  as  discussed  above.  Poly- 
technic flares  are  of  two  types — those  used  in  vertical  drops,  similar  to 
a  shotgun  shell  or  flare-pistol  cartridge,  and  the  end-burning  type, 
similar  to  warning  flares.  The  flares  contain  silver  iodide  with  or  with- 
out an  auxiliary  oxydizer,  such  as  potassium  nitrate,  together  with 
aluminum,  magnesium,  and  synthetic  resin  binder.  Dropping  flares  are 

68  National  Academy  of  Sciences,  National  Research  Council,  Committee  on  Atmospheric 
Sciences,  "Weather  and  Climate  Modification  :  Problems  and  Progress,"  Washington,  D.C.. 
1973.  pp.  115-16. 

61  Ibid.,  p.  117. 

85  Ibid.,  pp.  118,  120. 

M  Ibid.,  pp.  119-120. 


intended  to  be  dropped  into  updrafts  and  to  seed  the  cloud  over  a  verti- 
cal depth  as  great  as  a  kilometer,  while  burner  seeding  is  intended  to  be 
more  controlled  and  gradual.  Hoppers  dispense  materials  in  solid  form, 
such  as  the  particles  of  dry  ice  crushed  and  dropped  into  clouds  and 
cold  fogs.  For  warm  fog  and  cloud  modification  hoppers  are  used  to 
dispense  dry  salt  or  urea.  Sometimes  these  materials  are  pumped  in  a 
solution  to  nozzles  in  the  wings,  where  the  wingtip  vortices  help  mix 
the  agent  into  the  air.67 

On  the  ground  there  are  a  number  of  seeding  modes  which  are  fre- 
quently used,  and  types  of  nucleants  used  with  ground-based  genera- 
tors are  commonly  of  two  types — a  complex  of  silver  iodide  and  sodium 
iodide  or  of  silver  iodide  and  ammonium  iodide.  Outputs  from  the  gen- 
erator are  usually  from  6  to  20  grams  per  hour,  although  generators 
with  much  greater  outputs  are  used  sometimes.  One  seeding  mode  in- 
volves dispensing  continuously  into  the  airstream  from  a  ground  gen- 
erator at  a  fixed  point,  the  approach  used  most  commonly  in  mountain- 
ous terrain.  If  the  generator  is  located  in  flat  country  at  temperatures 
above  freezing,  the  nucleation  level  is  reached  through  entrainment  of 
the  material  into  the  convection.68 

The  nucleating  effectiveness  of  silver  iodide  smoke  is  dependent  upon 
the  cloud  temperature,  where  the  colder  the  temperature  the  greater  is 
the  number  of  ice  crystals  formed  per  gram  of  silver  iodide.  Tests  of 
nucleating  effectiveness  are  made  in  the  Colorado  State  University 
cloud  simulation  facility,  where  the  nucleant  is  burned  in  a  vertical 
wind  tunnel  and  a  sample  of  the  aerosol  is  collected  in  a  syringe  and 
nucleant  density  calculated  from  the  pyrotechnic  burn  rate  and  the 
tunnel  flow  rate.  The  syringe  sample  is  diluted  with  clean,  dry  air  and 
injected  into  a  precooled  isothermal  cold  chamber  containing  cloud 
droplets  atomized  from  distilled  water.  Ice  crystals  which  grow  and 
settle  out  are  collected  on  microscopic  slides,  so  that  nucleating  effec- 
tiveness can  be  calculated  as  the  ratio  of  concentrated  crystals  detected 
to  the  mass  of  nucleating  material  in  the  air  sample.69 

As  part  of  the  preparations  for  the  1976  seeding  operations  in  the 
Florida  area  cumulus  experiment  (FACE)  of  the  National  Oceanic 
and  Atmospheric  Administration  (NOAA),  Sax  et  al.,  carefully 
evaluated  the  silver  iodide  effectiveness  of  different  flares  used  in 
FACE.  The  results  of  these  effectiveness  studies,  conducted  with  the 
Colorado  State  University  facility,  are  shown  in  figure  14.  It  was  dis- 
covered that  a  newly  acquired  airborne  flare,  denoted  as  NEI  TB-1 
in  the  figure,  was  considerably  more  effective  than  both  the  Navy 
flares  used  earlier  and  another  commercially  available  flare  (Olin 
WM-105).  The  superiority  of  the  NEI  TB-1  material  at  warmer 
temperatures  is  particularly  noteworthy.70  In  another  paper,  Sax, 
Thomas,  and  Bonebrake  observe  that  crystalline  ice  concentrations  in 
clouds  seeded  in  FACE  during  1976  with  the  NEI  flares  greatly 
exceeded  those  found  in  clouds  seeded  during  1975  with  Navy  flares. 

67  Ruskin,  R.  E.  and  W.  D.  Scott,  "Weather  Modification  Instruments  and  Their  Use." 
In  Wilmot  N.  Hess  (ed.),  "Weather  and  Climate  Modification,"  New  York,  Wiley,  1974,  pp. 

68  Elliott,  Robert  D.,  "Experience  of  the  Private  Sector."  In  Wilmot  N.  Hess  (ed.), 
"Weather  and  Climate  Modification,"  New  York,  Wilev,  1974,  p.  57. 

09  Sax,  Robert  I..  Dennis  M.  Garvey,  Farn  P.  Parungo,  and  Tom  W.  Slusher,  "Characteris- 
tics of  the  Agl  Nucleant  Used  in  NOAA's  Florida  Area  Cumulus  Experiment."  In  preprints 
of  the  "Sixth  Conference  on  Planned  and  Inadvertent  Weather  Modification,"  Champaign, 
111.,  Oct.  10-13.  1977.  American  Meteorological  Society,  Boston,  1977,  p.  198. 

70  Ibid.,  pp.  198-201. 


They  conclude  that,  if  differences  in  sampling  time  intervals  and  effects 
of  instrumentation  housing  can  be  ignored,  there  is  indicated  a  much 
greater  nucleation  effectiveness  for  the  XEI  flares  which  were  used 
predominantly  after  July  1975.71  The  implications  of  this  result  are 
very  far  reaching,  since  the  borderline  and/or  slightly  negative  results 
of  many  previous  experiments  and  operational  projects1  can  possibly 
be  laid  to  the  ineffectiveness  of  the  silver  iodide  flares  previously 

0        -5        -10       -15  -20 

Figure  14. — Effectiveness  of  various  silver  iodide  flares  in  providing  artificial 
nuclei  as  a  function  of  cloud  temperature.  The  principal  comparison  is  between 
the  XEI  TB-1  and  the  Navy  TB-1  flares  (see  text)  ;  the  curve  of  mean  data  for 
the  Olin  WM-105  flares  is  included  for  comparison.  The  curves  show  that  the 
XEI  flares,  used  In  FACE  in  late  1975  and  1976  were  significantly  more  effec- 
tive in  producing  nuclei  at  warmer  temperatures  just  below  freezing.  ( From 
Sax,  Garvey,  Parungo,  and  Slusher,  1977.) 


There  has  been  much  emphasis  on  evaluation  methodology  on  the 
part  of  weather  modification  meteorologists  and  statisticians,  partic- 
ularly with  regard  to  precipitation  modification.  Progress  in  this 

71  Sax.  Robert  I..  Jack  Thomas.  Marilyn  Bonebrake.  "Differences  in  Evolution  of  Ice 
Within  Seeded  and  Nonseeded  Florida  Cumuli  as  a  Function  of  Nucleating  Agent."  In  pre- 
prints of  the  "Sixth  Conference  on  Planned  and  Inadvertent  Weather  Modification. "  Cham- 
paign, 111.,  Oct.  10-13,  1977.  Boston,  American  Meteorological  Society,  1977,"  pp.  203-205. 


area  has  been  slow,  owing  to  the  complexity  of  verification  problems 
and  to  inadequate  understanding  of  cloud  physics  and  dynamics. 

Having  reviewed  previous  considerations  of  evaluation  attempts, 
Changnon  discovered  a  wide  variety  of  results  and  interpretations, 
noting  that  "a  certain  degree  of  this  confusion  has  occurred  because 
the  methods  being  used  were  addressed  to  different  purposes  and 
audiences,  and  because  there  has  been  no  widely  accepted  method  of 
verification  among  investigators."  72  He  continues : 

For  instance,  if  one  considers  identification  of  changes  in  the  precipitation 
processes  most  important  to  verification  of  modification  efforts,  then  he  will 
often  undertake  evaluation  using  a  physical-dynamic  meteorological  approach. 
If  he  considers  statistical  proof  of  surface  precipitation  changes  the  best  method, 
he  may  concentrate  verification  solely  on  a  statistical  approach  or  make  in- 
adequate use  of  the  physical  modeling  concepts.  On  the  other  hand,  if  the  evalua- 
tion is  to  satisfy  the  public,  the  consumer,  or  the  governmental  decision-maker, 
it  must  be  economic-oriented  also.  Hence,  a  review  of  the  subject  of  previous 
evaluation  methodology  must  be  constantly  viewed  with  these  different  goals 
and  concepts  in  mind.73 

Evaluation  methodology  for  weather  modification  must  deal  with 
three  fundamental  problems  which  Changnon  has  identified : 74 

1.  There  are  many  degrees  of  interaction  among  atmospheric  forces 
that  result  in  enormous  variability  in  natural  precipitation,  greatly 
restricting  attempts  for  controlled  experiments  that  are  attainable 
in  other  physical  and  engineering  sciences. 

2.  There  is  an  absolute  need  to  evaluate  weather  modification  with 
statistical  procedures;  this  requirement- will  exist  until  all  underlying 
physical  principles  of  weather  modification  can  be  explained. 

3.  The  data  used  in  the  evaluation  must  be  sufficiently  adequate  in 
space  and  time  over  an  experimental  region  to  overcome  and  describe 
the  natural  variability  factors,  so  that  a  significant  statistical  signal 
may  be  obtained  within  the  noise  of  the  variability. 

It  is  further  recognized  that  analysis  of  weather  modification  ex- 
periments is  closely  akin  to  the  weather  prediction  problem,  since 
evaluation  of  weather  modification  efforts  is  dependent  on  a  com- 
parison of  a  given  weather  parameter  with  an  estimate  of  what  would 
have  happened  to  the  parameter  naturally.  Thus,  the  better  the  pre- 
diction of  natural  events,  the  better  can  a  weather  modification  proj- 
ect be  designed  and  evaluated,  at  the  same  time  reducing  the  verifica- 
tion time  required  by  a  purely  statistical  approach.75 

Initially,  weather  modification  evaluation  techniques  used  only  the 
observational  or  "look  and  see"  approach,  improved  upon  subsequently 
by  the  "percent  of  normal"  approach,  in  which  precipitation  during 
seeding  was  compared  with  normals  of  the  pre-experimental  period. 
Later,  using  fixed  target  and  control  area  data  comparisons,  regres- 
sion techniques  were  attempted,  but  the  high  variability  of  precipita- 
tion in  time  and  space  made  such  approaches  inapplicable.  In  the 
mid-1960's  there  was  a  shift  in  sophisticated  experiments  toward 
use  of  randomization.  In  a  randomized  experiment,  seeding  events 
are  selected  according  to  some  objective  criteria,  and  the  seeding 
agent  is  applied  or  withheld  in  sequential  events  or  adjacent  areas 

72  Changnon.  Stanley  A..  Jr..  "A  Review  of  Methods  to  Evaluate  Precipitation  Modifica- 
tion in  North  America."  Proceedings  of  the  WMO/IAMAP  Scientific  Conference  on  Weather 
Modification.  Tashkent.  U.S.S.R..  Oct.  1-7,  1973,  World  Meteorological  Organization. 
WMO— No.  399.  Geneva,  1974,  p.  397. 

73  Ibid.,  p.  398. 

74  Ibid. 

75  Ibid. 


in  accordance  with  a  random  selection  scheme.  An  inherent  problem 
with  randomization  is  the  length  of  experimental  time  required; 
consequently,  the  approach  is  not  often  satisfying  to  those  who  wish 
to  obtain  maximum  precipitation  from  all  possible  rain  events  or 
those  who  want  to  achieve  results  in  what  appears  to  be  the  most 
economical  manner.  As  a  result,  commercial  projects  seldom  make 
use  of  randomization  for  evaluation,  and  such  techniques  are  gen- 
erally reserved  for  research  experiments.76 

In  very  recent  years  the  randomization  approach,  which  to  many 
appeared  to  be  too  "statistical"  and  not  sufficiently  meteorological 
in  character,  has  been  improved  on  through  a  better  understanding 
of  atmospheric  processes,  so  that  a  physical-statistical  approach  has 
been  adopted.77 

Changnon  reviewed  approximately  100  precipitation  modification 
projects  in  North  America  and  found  essentiallv  6  basic  methods 
that  have  been  employed  in  project  evaluations.  He  identified  these 
as  (1)  direct  observation  (usually  for  single  element  seeding  trials), 
(2)  one-area  continuous  with  no  randomization  (involving  historical 
and/or  spatial  evaluation),  (3)  one-area  randomization,  (4)  target- 
control  area  comparisons,  (5)  cross-over  with  randomization,  and 
(6)  miscellaneous.78  These  methods,  along  with  the  kinds  of  data 
which  have  been  used  with  each,  are  listed  in  table  9. 



(From  Changnon,  "A  Review  of  Methods  to  Evaluate  Precipitation  Modification  in  North  America,"  1974] 



precipitation  data 

elements  data 

economic  data 

Direct  observation  Change  in  type;  duration 

of  precioitation;  areal 
distribution  (vs.  model) 

One-area  continu-     Historical  Area-rain  regressions; 

ous  (nonrandom).  weekend-weekday 

rainfall  differences; 
frequency  of  rain 

Spatial   Area-rain  regressions; 

pattern  recognition; 
trend  surfaces;  rain 
rates;  raindrop  sizes; 
frequency  of  rain 
days;  rain  cell  differ- 
ences; precipitation 
type  change;  areal 
extent  of  rain. 

Target  control  Area  rainfall  (day, 

month,  season)  repres- 
sions; area  snowfall 
(day,  month,  season). 
One-area  ran-  Basically  Area  precipitation; 

domized  (hours        statistical.  plume  area  precipi- 

pulsed).  tation:  change  in  pre- 

cipitation type.  Period 
Physical  plus         precipitation;  echo 
statistical.         area;  rain  rates;  echo 
reflectivity;  rain 

Crossover  ran-  Area  rainfall;  zonal 

dnmized.  rainfall. 

Miscellaneous  (post  

hoc  stratifica- 

Cloud  parameters;  echo 
parameters;  seed  and 

Frequency  of  severe        Added  runoff;  crop 
weather;  frequency         yields;  ecological, 
of  smoke  days. 

Synoptic  weather  con-     Runoff  increases;  crop 
ditions;  cloud  parame-     yields;  ecological, 
ters;  echo  parameters; 
Agl  plums;  nuclei 
sources;  airflow- 
plume  behaviors; 
tracers  in  rain;  atmos- 
pheric electrical 

Echo  parameters  Runoff  regressions. 

Synoptic  weather  con- 
ditions; cloud  parame- 
ters; seed  material  in 
plumes.  Fcho  parame- 
ters; Agl  in  rain;  cloud 
numerical  models; 
storm  behavior; 
cloud  base  rain  rate. 

Synoptic  types  and 
upper  air  conditions. 

Upper  air: 

1.  Temperature. 

2.  Winds. 

3.  Moisture  stability 

Synoptic  weather  types. 

Water  yield;  runoff; 
ecosystem  (plant  and 
animals)  and  erosion; 
avalanche— disbene- 

76  Ibid.,  p.  399. 

77  Ibid.,  p.  400. 

78  Ibid.,  p.  407. 


The  direct  observation  technique  was  the  first  major  approach  to 
evaluation  and  is  still  used  occasionally.  In  addition  to  direct  observa- 
tion of  the  change  and  type  of  precipitation  at  the  surface,  the  time  of 
precipitation  initiation,  and  areal  distribution  following  treatment  of 
a  cloud  or  cloud  group,  other  meteorological  elements  have  been  ob- 
served ;  these  include  radar  echo  characteristics,  plume  of  the  seeding 
material,  and  cloud  parameters  (microphysical  properties  and  dynam- 
ical and  dimensional  properties  such  as  updrafts,  cloud  size,  and  rate 
of  growth.).79 

The  one-area  continuous  (nonrandomized)  techniques  have  been 
employed  to  evaluate  many  of  the  commercially  funded  projects  in 
North  America,  recent  efforts  to  investigate  inadvertent  precipitation 
modification  by  large  urban-industrial  areas,  and  the  statewide  South 
Dakota  seeding  program.  This  category  includes  the  largest  number 
of  projects,  and  control  data  for  these  nonrandomized  projects  have 
included  both  historical  data  and  data  from  surrounding  areas.  The 
uncertainty  of  the  control  data  as  a  predictor  of  target  data  is  the  basic 
problem  in  using  this  approach.80 

*  Most  federally  sponsored  weather  modification  projects  have  used 
the  one-area  randomization  method,  which  involves  the  use  of  a  variety 
of  precipitation  elements,  including  duration,  number  of  storms,  and 
storm  days  and  months.  Projects  evaluated  with  this  method  fall  into 
two  categories,  including,  as  shown  in  table  9,  those  using  the  basic 
statistical  approach  and  the  more  recent  physical  plus  statistical  tech- 
niques. The  latter  group  of  projects  have  been  based  on  a  greater 
knowledge  of  cloud  and  storm  elements,  using  this  information  in 
defining  seedable  events  and  combining  it  with  statistical  tests  to  detect 
effects.  Surface  data,  including  rainfall  rates  and  area  mean  rainfall 
differences,  are  used  to  evaluate  such  one-area  randomized  projects.81 

The  target-control  method  involves  a  single  area  that  is  seeded  on 
a  randomized  basis  and  one  or  more  nearby  control  areas  that  are  never 
seeded  and,  presumably,  are  not  affected  by  the  seeding.82  The  method 
had  been  used  in  about  10  North  American  projects  through  1974. 
Evaluation  data  have  been  mostly  area  rainfall  or  snowfall  regres- 
sions, runoff  differences,  and  radar  echo  parameter  changes.83 

The  crossover  (with  randomization)  method  has  been  considered 
by  many  to  be  the  most  sophisticated  of  the  statistical  evaluation 
methods.  The  crossover  design  includes  two  areas,  only  one  of  which 
is  seeded  at  a  time,  with  the  area  for  seeding  selected  randomly  for 
each  time  period.  As  with  the  target-control  method,  a  problem  arises 
in  this  method  in  that  there  is  the  possibility  of  contamination  of  the 
control  areas  from  the  seeded  area.84  In  the  single  project  to  which  the 
method  had  been  applied  up  to  1974,  the  evaluation  procedure  involved 
classification  of  potential  treatment  events  according  to  meteorological 
conditions,  followed  by  area  and  subarea  rainfall  comparisons.85  The 

so  Ibid.,  pp.  408-409. 

81  Ibid.,  p.  409.  „  .   „  T 

82  Brier.  Glenn  W.  "Design  and  Evaluation  of  Weather  Modification  Experiments.  In 
Wilroot  N.  Hess  (editor),  "Weather  and  Climate  Modification,"  New  York.  Wiley,  iy74. 

P'  safhangnon.  "A  Review  of  Methods  To  Evaluate  Precipitaiton  Modification  in  North 
America."  1974.  p.  409.  ,       .   „'     Wil  01A 

84  Brier.  "Desiern  and  Evaluation  of  Weather  Modification  Experiments.   1974.  p.  210. 

ssChangnon.  "A  Review  of  Methods  To  Evaluate  Precipitation  Modification  in  Nortn 
America,"  1974,  p.  409. 


miscellaneous  methods  in  table  9  refer  basically  to  evaluation  efforts 
that  have  occurred  after  but  generally  within  the  context  of  the  five 
methods  mentioned  above,  and  have  been  largely  post-hoc  stratifica- 
tions of  results  classified  according  to  various  meteorological  subdivi- 
sions, followed  by  re-analysis  of  the  surface  rainfall  data  based  on 
these  stratifications.86 

IFrom  Changnon  "A  Review  of  Methods  to  Evaluate  Precipitation  Modification  in  North  America,"  1974] 


Surface  hail  data 

Meteorological  elements  Geophysical-economic 

Direct  observation  Cessation  of  hail;  hail  Echo  parameters;  cloud 

pattern;    hail    sizes  parameters;  Agl  in  hail. 

change;  hailstone 


One-area  continuous  Historical  Number  of  hail  days  


Spatial  Number  of  hail-produc-  Radar  echo  character- 
ing clouds/unit  time;  istics. 
hailstreak  frequencies; 
number  of  hail  days; 
rainfall  characteristics; 
impact  energy;  loca- 
tion of  hail  vs.  total 
precipitation  area. 

Target-control   Energy;  hail  day  frequen-  Radar  echo  characteris- 

cy.  tics. 

One-area   random-  Impact  energy;  hail  day  Radar  echo  characteris- 

ization.  frequency;      hailf all     tics;  Agl  in  hail-rain, 


Cross-over  random-  Energy;  area  of  hail;  vol-  Agl  in  hail, 

ized.  ume  of  hail. 

Crop-hail  loss  (insurance); 
insurance  ratej. 
Crop-hail  loss  (insurance) 

Hail  loss  (insurance). 

Ecosystem  (Agl);  crop- 
loss  data. 

About  20  projects  concerned  with  hail  modification  were  also  ana- 
lyzed by  Changnon  with  regard  to  the'  evaluation  techniques  used.  The 
five  methods  used,  shown  in  table  10,  include  the  first  five  methods 
listed  in  table  9  and  discussed  above  for  precipitation  modification 
evaluation.  A  comparison  of  tables  9  and  10  reveals  that  the  evaluation 
of  rain  and  snow  modification  projects  uses  much  less  variety  of  kinds 
of  data,  especially  the  meteorological  elements.  The  evaluation  of  hail 
projects  is  largely  statistical,  owing  to  the  lack  of  sophistication  in  the 
physical  modelling  of  hailstorms.  There  has  been  greater  use  of  eco- 
nomic data  in  hail  evaluation,  however,  than  in  evaluation  of  rainfall 
projects,  due  to  some  extent  to  the  lack  of  surface  hail  data  in  weather 
records  and  the  consequent  need  to  make  use  of  crop  insurance  data.87 

In  hail  evaluation,  the  direct  observation  method  has  been  used  to 
look  at  physical  effects  from  seeding  individual  storms  and  storm 
systems,  involving  analysis  of  time  changes  in  surface  hail  parameters, 
radar  echo  characteristics,  and  cloud  properties.  The  one-area  contin- 
uous (non-random)  method  has  been  the  principal  one  used  in  com- 
mercial hail  projects  and  in  studies  of  inadvertent  urban-industrial 
effects  on  hail,  using  historical  and/or  spatial  data  in  the  evaluation. 
One  major  data  form  in  these  evaluations  is  the  crop-hail  loss  from 
insurance  data.  The  target-control  method  has  made  use  of  hail  fall 
enerjry,  hail-day  frequencies,  and  crop-hail  loss  as  evaluation  data.88 

»  Ibid. 

87  IMd.,  pp.  412-413. 

88  Ibid.,  p.  413. 


The  one-area  randomization  method  is  the  method  used  in  the  Na- 
tional Hail  Research  Experiment.89  Various  degrees  of  randomization 
have  been  used,  ranging  from  50-50  to  80-20 ;  however,  the  evaluation 
data  have  been  similar  to  those  used  in  other  methods.  Silver  concen- 
trations in  samples  of  rain  and  hail  and  elsewhere  in  the  ecosystem 
have  been  used  as  evaluation  criteria.  The  crossover  randomized 
method  of  evaluation  has  also  been  applied  to  hail  projects,  using  such 
data  as  areal  comparisons  of  impact  energy,  area  extent  of  hail,  and 
total  hail  volume,  noting  also  the  concentrations  of  seeding  material 
in  the  hailstones.90 

A  necessary  part  of  any  evaluation  scheme  involves  the  measurement 
or  estimation  of  the  amounts  of  precipitation  fallen  over  a  given  area 
following  seeded  or  control  storm  events.  Such  measurement  is  part  of 
a  more  general  requirement  as  well  in  collecting  data  for  validation 
of  weather  predictions,  development  of  prediction  models,  compilation 
of  climatic  records,  and  forecasting  of  streamrlowT  and  water  resources. 
Although  the  customary  approach  to  precipitation  measurement  has 
been  to  use  an  array  of  rain  gages,  weather  radars  have  proven  to  be 
useful  tools  for  studying  generally  the  spatial  structure  of  precipita- 
tion. Depending  on  the  quality  of  the  onsite  radar  system  calibration, 
there  have  been  varying  degrees  of  success,  however,  in  use  of  this 
tool.  Often  radar  and  rain  gage  data  are  combined  in  order  to  obtain 
the  best  estimate  of  precipitation  over  a  given  area.  In  this  arrange- 
ment, the  radar  is  used  to  specify  the  spatial  distribution  and  the 
gauges  are  used  to  determine  the  magnitude  of  the  precipitation.91 
.  Exclusive  use  of  rain  gauges  in  a  target  area  in  evaluation  of  con- 
nective precipitation  modification  projects  requires  a  high  gauge  den- 
sity to  insure  adequate  spatial  resolution.  For  a  large  target  area,  such 
an  array  would  be  prohibitively  expensive,  however,  so  that  weather 
radars  are  often  used  in  such  experiments.  The  radar  echos,  which 
provide  estimates  of  precipitation,  are  calibrated  against  a  relatively 
smaller  number  of  rain  gages,  located  judiciously  in  the  target  area 
to  permit  this  calibration. 

It  has  been  shown  that  adjusted  radar  estimates  are  sometimes 
superior  to  either  the  radar  or  the  gages  alone.  Furthermore,  the  best 
areal  estimates  are  obtained  using  a  calibration  factor  which  varies 
spatially  over  the  precipitation  field  rather  than  a  single  average 
adjustment.  Erroneous  adjustment  factors  may  be  obtained,  however, 
if  precipitation  in  the  vicinity  of  the  calibration  gage  is  so  highly 
variable  that  the  gage  value  does  not  represent  the'  precipitation 
being  sampled  by  the  radar.  The  technique  for  calculating  the  adjust- 
ment factor  typically  involves  dividing  the  gage  measurement  by  the 
summed  rainfall  estimates  inferred  from  the  radar,  to  obtain  the 
ratio,  G/E,  used  subsequently  to  adjust  radar  estimates  over  a  greater 

89  The  National  Hail  Research  Experiment  is  discussed  as  part  of  the  weather  modifica- 
tion program  of  the  Natonal  Science  Foundation,  ch.  5,  p.  274ff. 

90  Changnon,  "A  Review  of  Methods  To  Evaluate  Precipitation  Modification  in  North 
America,"  1974,  p.  413. 

91  Crane,  Robert  K.,  "Radar  Calibration  and  Radar-rain  Gauge  Comparisons."  In  pre- 
prints of  the  "Sixth  Conference  on  Planned  and  Inadvertent  Weather  Modification,"  Cham- 
paign, 111.,  Oct.  10-13,  1977.  Boston,  American  Meteorological  Society,  1977,  p.  369. 

92  Klazura,  Gerald  E.,  "Changes  in  Gage/radar  Ratios  in  High  Rain  Gradients  by  Varying 
the  Location  and  Size  of  Radar  Comparison  Area."  In  preprints  of  the  "Sixth  Conference 
on  Planned  and  Inadvertent  Weather  Modification,"  Champaign,  111.,  Oct.  10-13,  1977. 
Boston,  American  Meterological  Society,  1977,  p.  376. 


In  the  evaluation  of  hail  suppression  experiments,  or  measurements 
of  hailfall  in  general,  there  must  be  some  means  of  determining  the 
extent  and  the  magnitude  of  the  hail.  One  technique  is  to  use  a  net- 
work of  surface  instruments  called  hailpads.  Since  single  storms  can 
lay  down  hail  swaths  up  to  100  kilometers  long  and  tens  of  kilometers 
wide,  made  up  of  smaller  patches  called  "hailstreaks,"  the  spacings  of 
hailpads  must  be  reduced  to  a  few  hundred  meters  to  collect  quantita- 
tive data  over  small  areas.  Even  over  small  distances  of  the  order  of 
1  kilometer,  it  has  been  discovered  that  total  numbers  of  hailstones, 
hail  mass,  and  hail  kinetic  energy  can  vary  by  over  a  factor  of  10.93 
Another  means  of  estimating  hailfall  is  through  use  of  crop- damage 
studies.  Such  results  are  obtained  through  crop-loss  insurance  data, 
aerial  photography  of  damaged  fields,  and  combinations  of  these  data 
with  hailpad  measurements.94 


The  term  "extended  area  effects"  refers  to  those  unplanned  changes 
to  weather  phenomena  which  occur  outside  a  target  area  as  a  result  of 
activities  intended  to  modify  the  weather  within  the  specified  target 
area.  Such  effects  have  also  been  called  by  a  variety  of  other  names 
such  as  "downwind  effects,"  "large-scale  effects,"  "extra-area  effects," 
"off-target  effects,"  and  "total-area  effects."  When  the  time  dimen- 
sion is  considered,  those  changes  which  occur,  or  are  thought  to  have 
occurred,  either  within  the  spatial  bounds  of  the  target  area  or  in 
the  extended  area  after  the  intended  effects  of  the  seeding  should 
have  taken  place  are  referred  to  as  "extended  time  effects."  These 
inadvertent  consequences  are  usually  attributed  either  to  the  transport 
of  seeding  material  beyond  the  area  intended  to  be  seeded  or  the 
lingering  of  such  material  beyond  the  time  during  which  it  was  to  be 

In  a  number  of  experiments  there  have  been  indications  that  an 
extended  area  effect  occurred.  The  present  state  of  understanding  does 
not  permit  an  explanation  of  the  nature  of  these  effects  nor  have  the 
experimental  designs  provided  sufficient  information  to  describe  their 
extent  adequately.  The  subject  is  in  need  of  additional  study,  with 
experiments  designed  to  provide  more  specific  data  over  pertinent 
areal  and  time  scales.  In  recent  years  two  conferences  on  extended 
area  effects  of  cloud  seeding  have  been  convened.  The  first  conference, 
attended  by  18  atmospheric  scientists,  was  held  in  Santa  Barbara, 
Calif.,  in  1971  and  was  organized  by  Prof.  L.  O.  Grant  of  Colorado 
State  University  and  by  Kobert  D.  Elliott  and  Keith  J.  Brown  of 
North  American  Weather  Consultants.  Attendees  at  the  1971  seminar 
discussed  existing  evidence  of  extended  area  effects,  considered  the 
possible  means  of  examining  detailed  mechanisms  responsible  for 
the  effects,  and  debated  the  implications  for  atmospheric  water  re- 
sources management. 

A  second  workshop  was  held,  under  the  sponsorship  of  the  National 

63  Morgan,  Griffith  M.  and  Nell  G.  Towery.  "Surface  Hall  Studies  for  Weather  Modifica- 
tion." In  preprints  of  the  "Sixth  Conference  on  Planned  and  Inadvertent  Weather  Modi- 
fication," Champaign,  111.,  Oct.  10-13,  1977,  p.  384. 

»*  Ibid. 


Science  Foundation,  at  Colorado  State  University,  Fort  Collins,  Colo., 
Aug.  8-12, 1977.95  The  Fort  Collins  meeting  was  attended  by  44  partici- 
pants, composed  of  social  scientists,  observationists,  physical  scientists, 
modellers,  statisticians,  and  evaluators.  The  group  was  exposed  to  a 
mass  of  data  from  various  weather  modification  projects  from  all  over 
the  world  and  proposed  to  accomplish  the  following  objectives  through 
presentations,  workshop  sessions,  and  general  discussions : 

Renew  the  deliberations  of  the  Santa  Barbara  seminar. 

Expand  the  scope  of  participation  so  as  to  integrate  and  inter- 
pret subsequent  research. 

Better  define  the  importance  of  extended  spatial,  temporal,  and 
societal  effects  of  weather  modification. 

Prepare  guidelines  and  priorities  for  future  research  direction.96 
Extended  area  effects  have  special  importance  to  the  nontechnical 
aspects  of  weather  modification.  From  deliberations  at  the  1977 
extended  area  effects  workshop  it  was  concluded  that : 

The  total-area  of  effect  concept  adds  a  new  dimension  to  an  already  complex 
analysis  of  the  potential  benefits  and  disbenefits  of  weather  modification.  A  speci- 
fied target  area  may  have  a  commonality  of  interests  such  as  a  homogeneous  crop 
in  a  farm  area  or  a  mountain  watershed  largely  controlled  by  reservoirs  built  for 
irrigation  and/or  hydroelectric  power  generation.  Socioeconomic  analysis  of  this 
situation  is  much  more  direct  than  the  consideration  of  the  total-area  of  effect 
which  may  well  extend  into  areas  completely  dissimilar  in  their  need  or  desire  for 
additional  water.  The  spatial  expansion  of  the  area  of  effect  may  increase  or  de- 
crease the  economic  and  societal  justification  for  a  weather  modification  program. 
The  political  and  legal  consideration  may  also  be  complicated  by  this  expansion  in 
scope  since  effects  will  frequently  extend  across  state  or  national  borders.81 

The  strongest  evidence  of  extended  area  effects  is  provided  by  data 
from  projects  which  involved  the  seeding  of  wintertime  storm  systems. 
Statistical  analyses  of  precipitation  measurements  from  these  projects 
suggest  an  increase  in  precipitation  during  seeded  events  of  10  to  50 
percent  over  an  area  of  several  thousand  square  kilometers.  Some  of  the 
evidence  for  these  effects,  based  mostly  on  post  hoc  analyses  of  project 
data,  appears  fairly  strong,  though  it  remains  somewhat  suggestive  and 
speculative  in  general.98 

Based  upon  two  general  kinds  of  evidence:  (1)  observational  evi- 
dence of  a  chemical  or  physical  nature  and  (2)  the  results  of  large 
scale/long-term  analyses ;  a  workshop  group  examining  the  extended 
area  effects  from  winter  orographic  cloud-seeding  projects  assembled 
the  information  in  table  11.  It  should  be  noted  that  the  quality  of  the 
evidence,  indicated  in  the  last  column  of  the  table,  varies  from  "well 
documented"  and  "good  evidence"  to  "unknown"  and  "no  documenta- 
tion available;"  however,  the  general  kinds  of  extended  area  and 
extended  time  effects  from  a  number  of  winter  projects  are  illustrated.99 

95  Brown.  Keith  J.,  Robert  D.  Elliott,  and  Max  Edelstein,  "Transactions  of  Workshop  on 
Extended  Space  and  Time  Effect  of  Weather  Modification,"  Aug.  8-12,  1977,  Fort  Collins, 
Coio  North  American  Weather  Consultants,  Goleta,  Calif.,  February  1978.  279  pp. 

«*  Ibid.,  pp.  7-9. 

67  Ibid.,  p.  13. 

68  Ibid.,  p.  10. 

"Warburton,  Joseph  A..  "Extended  Area  Effects  From  Winter-orographic  Cloud  Seeding 
Projects,"  report  of  workshop  panel.  In  Keith  J.  Brown,  et  al.  "Transactions  of  Workshop 
on  Extended  Space  and  Time  Effects  of  Weather  Modification,"  Aug.  8-12,  1977,  Fort  Col- 
lins, Colo.  North  American  Weather  Consultants,  Goleta,  Calif.,  February  1978,  pp.  137-164. 



[From  Warburton,  19781 




Type  of  effect      of  effect           Area  of  effect  Mechanism 

Quality  of 

Ice  crystal  anvil  production  Spatial  and 
from  dry  ice  seeding  of  time, 
cumulus    clouds,  Blu3 
Mountains,  Australia. 


Persistence  of  ice  nuclei  at 
Climax— probably  Agl  for 
days  after  seeding. 

Transport  of  Agl  from  Climax  Spatial, 
generators  to  30  km  down- 

Silver  in  snow.Sierra  Nevada  do. 

and  Rockies— up  to  100  km 
from  generators. 

Produced  rain 
6-12  mm 
over  18-hour 

nuclei  con- 

30  N/liter 
(-20°  C). 

4  to  100X 

1500  km2  Cirrus  seeding  Documentation 

and  transport  needed  (is 

of  crystals  available), 
from  seeding 
with  C02. 

Unknown  Unknown   Well  documented 

(is  available). 

~40  km2  Transport  of  Few  aircraft 

nuclei.  observations. 

Pressure  reductions  in  seeded 
band  periods,  Santa  Bar- 

Cirrus  shield  produced  by 
airborne  seeding,  Warra- 
gamba,  Australia. 

Time  Max.  —2  mb. 


Up  to  25  per- 
cent of 
seeded  days. 

Continuum  from 

Continuum  from 


sites  < — 1000 

2000  km2(l 


Physical  trans- 
port of  Agl 
on  hydro- 
meter's con- 
taining Agl. 
Dynamic  heat 

Ice  crystal 
seeding  of 
lower  clouds. 

5  yr  of  observa- 

Fair  to  moderate 

needed  (is 


Projection  description    Type  of  effect 

Magnitude  of  effect    Area  of  effect 

Quality  of  evidence 

Spatial  30  percent  >  40- 

yr,  average,  3 
successive  yr. 

Time;  long-term        10  to  40  percent. 

Spatial  +25  percent. 

Victoria,  Australia,  drought 
relief— non-randomized. 

Warragamba  and  other  large- 
scale  experiments — Aus- 
tralia decrease  in  S/NS 
ratio  wth  years  of  experi- 
ment. 1 

Israel  I— randomized  north 
and  central  seeded. 

Santa  Barbara  band  seed-  do  +25  percent  (+50 

ing— randomized.  percent  in  bands). 

Santa  Barbara  storm  seeding  do  Unknown  

of  multiple  bands. 

Time  Seed/no  seed  ratios 

of  1.5  to  4  mean 
50  percent-in- 

Spatial   Unknown  analysis 


35,000  km2;  conti- 
nuum from  seed- 
ing sites. 

Artifact  of  analysis.. 

6,000  km2;  conti- 
nuum from  seed- 
ing sites. 

3,000  km2;  conti- 
nuum from  seed- 
ing sites. 


Santa  Barbara  duration  of 
seeded/nonseeded  bands. 

Climax  and  east  to  plains  of 
Colorado  using  "homo- 
geneous" data  base  deter- 
mined by  new  synoptic 

3,000  km2;  conti- 
nuum from  seed- 
ing sites. 

600  km*;  130  km 
east  of  Climax, 
30  to  50  km 
south  of  Denver. 

No  documentation 

Reanalysis  needed 
avoiding  ratios 
and  double  ratios. 

Reliable  records  for 

Moderately  well 


Good  evidence. 


'Tasmania  experiment  may  confirm  artifact. 

Examination  of  data  from  summertime  convective  cloud-seeding 
projects  reveals  "more  mixed"'  results  by  comparison  with  data  from 
wintertime  projects,  when  extended  area  effects  are  considered.  This 
general  conclusion  accords  with  the  mixed  results  from  evaluations 
of  convective  cloud  seeding  within  the  target  area.  It  was  concluded 
by  participants  on  a  panel  at  the  1977  Fort  Collins  workshop  that, 
for  summertime  convective  cloud  seeding,  there  are  statistical  evi- 
dences of  both  increases  and  decreases  in  the  extended  area,  though 
there  are  a  large  number  of  nonstatistically  significant  indications. 
Table  12  was  assembled  by  the  panel  to  summarize  the  characteristics 
of  these  effects  for  each  of  the  projects  examined.1 

1  Smith.  T.  B..  "Report  of  Panel  on  Rummer  Weather  Mortification."  In  Keith  J.  Brown 
et  al.,  "Transactions  of  Workshop  on  Extended  Spare  and  Time  Effects  of  Weather  Modi- 
fication." Aug.  8-12.  1077.  Eort  Collins,  Colo.  North  American  Weather  Consultants.  Goleta. 
Calif..  February  1978.  pp.  228-326. 




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It  was  the  general  consensus  of  the  1977  workshop  participants 
that  seeding  can  effect  precipitation  changes  over  relatively  large 
areas  which  extend  beyond  the  typical  target  area.  Such  changes  can 
be  positive  or  negative  and  may  be  of  the  same  sign  as  the  effect  in 
the  designated  target  area  or  of  opposite  sign.  For  example,  among 
summertime  projects  considered  the  Israeli  experiment  provided  sub- 
stantial evidence  for  positive  effects  in  the  target  and  in  the  extended 
areas  (see  table  12).  Project  Whitetop  and  the  Arizona  experiment, 
on  the  other  hand,  showed  strong  evidence  of  precipitation  decreases 
in  the  target  areas,  downwind,  and  in  surrounding  areas.  The  Florida 
area  cumulus  experiment  (FACE)  revealed  significant  rainfall  in- 
creases in  the  target  area,  but  seemed  to  show  decreases  in  surround- 
ing areas,  and  the  1969-1972  South  Dakota  project  demonstrated 
negative  seeding  effects  in  the  target  area  and  positive  effects  in  ex- 
tended areas.  Of  all  projects  reviewed,  however,  and  in  view  of  all  the 
differing  results  suggested,  the  combination  of  target-  and  extended- 
area  effects  which  appears  to  have  the  least  support  is  that  combina- 
tion most  likely  to  occur  to  many  lay  people,  i.e.,  increases  in  the  tar- 
get area  with  compensating  decreases  in  some  area  "downwind" — 
the  "robbing  Peter  to  pay  Paul"  analogy.2 

Statistical  evidence  of  extended  area  and  time  effects  seems  to  be 
reasonably  common;  however,  the  mechanics  causing  these  effects 
are  not  understood.  It  appears  that  there  may  be  a  number  of  mech- 
anisms which  come  into  play,  the  dominating  ones  operating  under 
various  storm  types  and  seeding  techniques.  In  some  projects  there 
is  evidence  that  seeding  intensified  the  storm  dynamically  through 
release  of  latent  heat  of  sublimation.  In  other  cases  silver  iodide  has 
been  transported  for  distances  of  100  kilometers  downwind  of  the 
seeding  area  and  has  persisted  for  several  days  in  the  atmosphere 
after  seeding.  Also  ice  crystals  produced  from  seeding  may,  in  turn, 
seed  lower  clouds  downwind.3 

With  particular  regard  to  extended  area  or  time  effects  in  cumulus 
seeding  experiments,  Simpson  and  Dennis  have  identified  the  follow- 
ing list  of  possible  causes : 

1.  Physical  transport  of  the  seeding  agent. 

2.  Physical  transport  of  ice  crystals  produced  by  a  seeding  agent. 

3.  Changes  in  radiation  and  thermal  balance,  as  for  example,  from 
cloud  shadows  or  wetting  of  the  ground. 

4.  Evaporation  of  water  produced. 

5.  Changes  in  the  air-earth  boundary,  such  as  vegetation  changes 
over  land  or  changes  in  the  structure  of  the  ocean  boundary  layer 
following  cloud  modification. 

6.  Dynamic  effects: 

(a)  Intensified  subsidence  surrounding  the  seeded  clouds,  com- 
pensating for  invigorated  updrafts. 

(b)  Advection  or  propagation  of  intensified  cloud  systems 
which  subsequently  interact  with  orography  or  natural 

(c)  Cold  thunderstorm  downdrafts,  either  killing  local  convec- 
tion or  sotting  off  new  convection  cells  elsewhere. 

sp.rnwn.  et  nl.,  "Trnnsnotions  of  the  Workshop  on  Extended  Space  and  Time  Effects  of 
Weather  Mortification."  1978,  p.  11. 
'  Ihid..  p.  12. 


(d)  Extended  space-time  consequences  of  enhancement  or  sup- 
pression of  severe  weather  owing  to  cumulus  modification. 

(e)  Alteration,  via  altered  convection,  of  wind  circulation  pat- 
terns and/or  their  transports  which  could  interact  with  other  cir- 
culations, perhaps  at  great  distances.4 

Kecommended  research  activities  to  further  explore  and  develop 
understanding  of  extended  area  and  extended  time  effects  of  weather 
modification  are  summarized  in  the  final  section  of  this  chapter,  along 
with  other  research  recommendations.5 


Nearly  all  of  the  techniques  discussed  earlier  for  modifying  the 
weather  involve  some  kind  of  "cloud  seeding."  The  exception  is  in  the 
case  of  warm  fog  dispersal,  where  attempts  to  dissipate  have  also 
included  mechanical  mixing  or  application  of  heat.  While  most  cloud- 
seeding  techniques  involve  the  use  of  artificial  ice  nuclei  such  as  those 
provided  by  silver  iodide  particles,  other  "seeding"  substances,  such 
as  dry  ice,  sodium  chloride,  urea,  propane,  and  water  spray,  have  been 
used  in  certain  applications.  Clouds  have  also  been  seeded  with  metal- 
ized  plastic  chaff  in  order  to  dissipate  electrical  charge  build-up  and 
reduce  the  incidence  of  lightning. 

There  may  also  be  some  promise  in  future  years  of  beneficially 
changing  the  weather,  over  both  large  and  small  scales  of  time  and 
space,  using  technologies  that  are  not  in  the  general  category  of  cloud 
seeding.  Indeed,  some  such  schemes  have  been  proposed  and  there  has 
been  research  conducted  on  a  number  of  these  possibilities. 

In  the  following  chapter  the  effects  of  man's  activities  and. some  nat- 
ural phenomena  in  changing  the  weather  unintentionally  will  be  dis- 
cussed. While  these  inadvertent  effects  may  be  of  general  concern  and 
should  be  studied  in  view  of  potential  dangers,  they  should  also 
be  understood  inasmuch  as  they  may  provide  valuable  clues  on  how 
the  atmosphere  can  be  more  efficiently  modified  for  beneficial  purposes. 
For  example,  major  heat  sources  judiciously  located  might  be  used 
to  affect  weather  in  ways  useful  to  man. 

Solution  of  problems  which  overlap  considerations  of  both  weather 
and  energy  could  be  investigated  and  solved  in  common  by  scientists 
and  engineers  working  in  both  fields.  Such  research  should  be  under- 
way and  some  practical  applications  could  be  forthcoming  during 
the  1980's.  Dissipation  of  supercooled  clouds  and  fog  over  large  and 
medium-sized  cities,  which  now  appears  to  be  technically  feasible,  may 
become  desirable  when  solar  energy  collectors  are  more  common.  Ee- 
duction  of  radiative  losses  to  space  could  be  facilitated  by  allowing 
the  clouds  to  reform  at  night.  It  is  speculated  that  this  diurnal  cycle 
of  operation  would  tend  to  weaken  inversions  that  are  often  associated 
with  fog  and  low  stratus  and  so  tend  to  alleviate  problems  of  air 
pollution,  though  there  might  be  some  increase  of  photochemical 
effects  in  the  daytime  with  additional  sunlight.6 

Excess  heat  and  moisture  from  nuclear  and  other  powerplants  and 
from  their  cooling  towers  could  be  usefully  employed  for  generating 

4  Simpson  and  Dennis,  "Cumulus  Clouds  and  Their  Modification,"  19,74,  pp.  274-277. 

5  See  p.  143. 

6  Dennis  and  Gagln,  "Recommendations  for  Future  Research  In  Weather  Modification," 
1977,  p.  79. 


clouds  if  the  plants  are  optimally  located  with  regard  to  water  sources 
and  meteorological  conditions.  The  clouds  so  formed  might  be  used  for 
protection  to  crops  during  periods  of  intense  heat  or  as  a  shield  over  a 
city  at  night  to  prevent  re-radiation  of  heat  back  to  space.  The  clouds 
might  also  be  seeded  subsequently  somewhere  downwind  of  the  power- 
plant  to  enhance  precipitation. 

Recently,  Simpson  reviewed  and  summarized  the  state  of  research 
and  development  of  a  number  of  the  nonseeding  approaches  to  weather 
modification  which  have  been  proposed.7  She  discusses  effects  of 
changes  to  radiation  and  to  sea-air  interface  processes : 

Some  expensive,  brute  force  successes  have  been  obtained  by  burning  fuels  to 
clear  fogs  or  even  to  create  clouds.  A  more  ingenious  approach  is  to  use  solar  heat 
to  alter  part  of  the  air-surface  boundary  or  a  portion  of  the  free  atmosphere. 
Black  and  Tarmy  (1963)  proposed  ten  by  ten  kilometer  asphalt  ground  coatings 
to  create  a  "heat  mountain"'  to  enhance  rain,  or  to  reduce  pollution  by  breaking 
through  an  inversion.  Recently  Gray,  et  al.  (1975)  have  suggested  tapping  solar 
energy  with  carbon  dust  over  100-1,000  times  larger  areas  for  numerous  weather 
modification  objectives  ranging  from  rain  enhancement  to  snow  melt,  cirrus  pro- 
duction, and  storm  modification.  The  physical  hypotheses  have  undergone  pre- 
liminary modelling  with  promising  results,  while  the  logistics  appear  marginally 
feasible.  Drawbacks  are  the  unknown  and  uncontrollable  transport  of  the  dust 
and  its  environmental  unattractiveness. 

A  cleaner  way  of  differentially  heating  the  air  appears  to  be  a  possible  future 
byproduct  of  the  space  program.  A  Space  Solar  Power  Laboratory  is  in  the  plan- 
ning stages  at  NASA.  Its  main  purpose  is  to  provide  electric  power,  which  will 
be  sent  by  the  space  laboratory  to  the  earth's  surface.  The  microwave  power 
will  be  converted  to  DC  by  means  of  groups  of  rectifying  antennas,  which  dissi- 
pate a  fraction  of  the  power  into  heat.  Preliminary  calculations  *  *  *  indicate  that 
the  atmospheric  effect  of  the  estimated  heating  would  be  comparable  to  that  by 
a  suburban  area  and  thus  could  impact  mesoscale  processes.  Future  systems 
could  dissipate  much  more  heat  and  could  conceivably  be  a  clean  way  to  modify 
weather  processes.  It  is  not  too  soon  to  begin  numerical  simulation  of  atmospheric 
modifications  that  later  generation  systems  of  this  type  might  be  able  to  achieve. 

Radiation  alteration  appears  to  be  a  hopeful  weather  modification  approach 
still  lacking  a  developed  technology.  A  cirrus  cover  has  long  been  welcomed  as 
natural  frost  protection  when  it  restricts  the  nocturnal  loss  of  long-wave  radia- 
tion. More  recently,  the  effect  of  cirrus  in  cutting  off  short-wave  daytime  radia- 
tion has  been  modelled  and  measured.  *  *  *  Artificial  simulation  of  cirrus  effects 
by  minute  plastic  bubbles  impregnated  with  substances  to  absorb  selected  wave- 
lengths received  preliminary  attention  .  .  .  but,  to  my  knowledge  has  not  been 

Alteration  of  the  sea-air  interface  is  also  a  potentially  promising  weather 
modification  technique,  particularly  to  suppress  convection  or  to  mitigate  the  de- 
struction by  tropical  hurricanes.  However,  the  technology  in  this  area  may  be 
farther  from  actual  field  trials  than  that  in  radiation.  If  methods  could  be  de- 
veloped to  restrict  sea-air  latent  and  sensible  heat  flux,  the  development  from 
tropical  storm  to  hurricane  might  be  inhibited,  while  not  losing  rainfall  or  other 
benefits  of  the  system.  Presently  the  monomolecular  films  which  cut  down  the 
evaporation  from  reservoirs  do  not  stay  intact  in  oceanic  storm  conditions,  even 
if  the  logistics  of  their  delivery  over  wide  areas  ahead  of  the  storm  were  solved. 
Logistic  obstacles  have  also  impeded  implementation  of  the  promising  idea  of 
cooling  the  waters  ahead  of  the  hurricane  by  mixing  up  the  ocean  layer  above  the 

One  possible  means  of  achieving  the  mixing  of  ocean  layers  to  cool 
the  sea  surface,  suggested  above  by  Simpson,  might  be  accomplished, 

7  Simpson.  Joanne,  "What  Weather  Modification  Needs."  1977,  unpublished,  pp.  13--1.". 
(Most  of  the  needs  of  weather  modification  identified  In  this  unpublished  paper,  but  not 
including  her  summary  of  nonseeding  approaches,  were  published  in  another  paper  with 
the  same  title  by  Dr.  Simpson  :  preprints  of  "Sixth  Conference  on  Planned  and  Inadvertent 
Weather  Modification."  Champaign,  111.,  Oct.  10-13.  1977.  Boston,  American  Meteorological 
Society.  1977,  pp.  304-307. 

8  Ibid. 


at  least  in  part,  as  a  beneficial  byproduct  of  another  power  source 
under  development — the  ocean  thermal  energy  conversion  (OTEC) 
concept.  The  OTEC  plants,  located  in  tropical  waters  where  hurri- 
canes are  spawned  and  grow,  can  provide  surface  cooling  and  so  assist, 
at  least  in  localized  areas,  in  the  abatement  of  tropical  storms  and  their 
attendant  damages.  This  is  another  area  of  overlap  between  energy 
and  weather  interests  where  cooperative  research  and  development 
ought  to  be  explored. 

Research  Needs  for  the  Development  of  Weather  Modification 

In  previous  sections  of  this  chapter  the  rationale  and  the  status  of 
development  of  the  various  techniques  used  to  modify  several  kinds  of 
weather  phenomena  were  summarized  and  discussed  in  some  detail. 
Applications  of  these  techniques  in  both  operational  and  research  proj- 
ects were  considered  and  some  measures  of  the  current  effectiveness 
were  presented.  Among  these  discussions  were  a  variety  of  statements, 
some  explicit  and  some  implied,  on  further  research  necessary  to  ad- 
vance weather  modification  technology.  This  section  addresses  re- 
search needs  more  generally  and  in  a  more  sysf'matic  manner. 
Included  are  specific  requirements  and  recommendations  identified  by 
individual  experts  and  organizations.  Recommendations  of  a  policy 
nature  on  weather  modification  research,  such  as  the  role  of  the  Federal 
Government  and  the  organizational  structure  for  managing  research, 
are  discussed  in  chapter  6,  which  summarizes  the  recommendations  of 
major  policy  studies.  Current  research  programs  of  Federal  agencies 
are  discussed  in  some  detail  in  chapter  5. 

Research  recommendations  summarized  in  this  section  are  primarily 
concerned  with  advancing  the  technology  of  advertent  weather  modi- 
fication intended  for  beneficial  purposes.  Research  needs  in  support 
of  other  aspects  of  planned  weather  modification  and  on  inadvertent 
modification  are  included  in  other  chapters  on  those  subjects.  In  some 
cases,  however,  in  the  following  sets  of  recommendations,  research 
efforts  in  these  other  areas  are  included  with  those  dealing  with  tech- 
nology improvement  in  order  to  preserve  the  completeness  of  the  par- 
ticular set  of  recommendations. 

general  considerations 

Peter  Hobbs  identifies  four  main  phases  through  which  most  devel- 
oping technologies  such  as  weather  modification  must  pass — the  estab- 
lishment of  scientific  feasibility,  engineering  development,  demonstra- 
tion projects,  and  full-scale  plant  operation.9  He  illustrates  these 
phases  in  terms  of  relative  expenditures  and  elapsed  time  for  each  in 
figure  15  and  discusses  the  probable  stage  of  development  for  weather 
modification.  Noting  that  some  would  optimistically  place  develop- 
ment of  the  technology  as  far  along  as  the  dashed  line  YY,  he  himself 
would  more  cautiously  place  the  progress  of  weather  modification  in 
the  vicinity  of  XX,  so  that  the  major  task  ahead  remains  as  the  testing 
of  the  scientific  feasibility  to  produce  significant  artificial  modification 
to  the  weather.10 

9  Hobbs,  Peter  V.,  "Weather  Modification  ;  a  Brief  Review  of  the  Current  Status  and  Sug- 
gestion for  Future  Research."  Background  paper  prepared  for  the  U.S.  Department  of  Com- 
merce Weather  Modification  Advisory  Board,  March  1977,  p.  10. 

10  Ibid. 


This  scientific  feasibility  can  best  be  shown,  according  to  Hobbs, 
through  "mounting  comprehensive  research  programs  to  investigate 
the  structure  and  natural  processes  which  dominate  a  few  relatively 
simple  cloud  and  precipitation  systems  and  to  establish  the  extent  and 
reliability  with  which  they  can  be  artificially  modified."  He  cites  as  a 
principal  reason  for  the  lack  of  significant  progress  in  recent  years  his 
contention  that  "most  of  the  effort  has  been  directed  at  attempts  to 
modify  very  complicated  storm  systems  about  which  little  is  known 
and  good  hypotheses  for  artificial  modification  are  lacking."  11 


Figure  15. — Schematic  of  the  relative  costs  and  time  associated  with  the  four 
phases  of  development  of  a  new  technology.  The  vertical  lines  XX  and  YY 
indicate  two  widely  differing  views  on  the  present  stage  of  development  of 
weather  modification  technology.  (From  Hobbs,  1977.) 

We  have  seen  that  there  is  some  reason  to  accept  weather  modifica- 
tion techniques  as  having  some  degree  of  operational  capability  in 
possibly  two  areas — cold  fog  dispersal  and  snowfall  enhancement  from 
orographic  clouds — though  there  is  room  for  continued  research  and 
technique  development  in  these  as  well  as  other  areas  of  weather  modi- 
fication. Although  supercooled  fogs  accoimt  for  only  5  percent  of  all 
fog  occurrences,  their  prevalence  at  airports  in  northeastern  and 
northwestern  North  America  makes  cold  fog  dispersal  a  valuable  tool. 
Seeding  of  wintertime  orographic  clouds  in  experiments  and  opera- 
tional projects  in  the  western  United  States  has  probably  resulted  in 
snowfall  increases  of  10  to  30  percent  under  cert  am  conditions. 

Table  13  is  a  review  and  general  outlook  on  weather  modification, 
prepared  by  Ohangnon,  showing  the  stage  of  development,  possible 
economic  value  or  years  before  operational  usefulness,  and  status  of 
research  for  5  areas  of  weather  modification,  for  the  cold-tempera- 
ture  and  warm -temperature  cases  where  applicable.  The.  table  also 
shows  Changnon's  rough  estimate  of  the  complexity  and  difficulty  in 

11  Ibid.,  pp.  10-12. 


relation  to  fog  dispersal  of  the  development  of  modification  techniques 
for  the  other  phenomena.12 

Changnon  emphasizes  the  fact  that  established  techniques  do  not 
exist  for  significant  modification  of  weather  phenomena  such  as  rain- 
fall and  severe  weather  over  the  more  populous  and  major  agricul- 
tural areas  of  the  eastern  United  States.  He  says  that : 

If  measurable  economic  gains  are  to  be  realized  in  the  eastern  two-thirds  of 
the  United  States  due  to  weather  modification  (largely  rain  "management",  hail 
suppression,  and  abatement  of  severe  winter  storms),  much  more  research  and 
effort  must  be  extended.  This  research  will  concern  (1)  the  thorough  study  on 
a  regional  scale  of  the  complex  multicellular  convective  systems  which  are  the 
major  warm  season  rain  and  hail  producers,  and  (2)  the  study  of  the  cold  season 
cyclonic  systems.13 

[From  Changnon,  "Present  and  Future  of  Weather  Modification;  Regional  Issues,"  "75] 




Severe  convective  Cyclonic  scale 
storms  storms 

Cold  temperatures  Operational  phase; 
«32°F).  low  cost; 


Operational  phase    Research  phase; 
(+10  to  +30        favorable  on 

percent);  low 
cost;  research 

small  clouds; 
questionable  on 
large  clouds 
and  systems; 

Research  phase; 
5  to  10  yrs 
before  opera- 
tional; sub- 
stantial and 

Warm  tempera-     Research  phase; 
tures  (>32°  F).     2  to  5  yrs:  sub- 
stantial and 

Possible  phase;      Exploratory  phase; 
little  research.1  modest 

Degree  of  1.0. 
complexity  (in 
relation  to  fog). 




Exploratory  phase; 
more  than  10 
yrs;  research  on 
tropical  is 
modest;  research 
on  "other" 
storms  is  minor. 


Questionable  economic  value  unless  chain  reaction  is  found. 

Hobbs  discusses  in  detail  some  of  the  kinds  of  weather  modification 
research  projects  which  he  feels  would  be  fruitful : 

Some  candidate  projects  for  intensive  investigation  include  the  dispersal 
of  cold  and  warm  fogs,  the  enhancement  of  precipitation  from  isolated  conti- 
nental-type cumulus  clouds,  and  the  targeting  of  winter  orographic  snowfalls. 
Our  knowledge  of  each  of  these  subjects  has  reached  the  stage  where  the  mounting 
of  comprehensive  projects  is  likely  to  yield  definitive  results.  Physical  studies 
have  demonstrated  that  cold  fogs  can  be  dissipated  by  seeding  with  dry  ice,  and 
this  technique  is  now  in  use  operationally  at  a  number  of  airports ;  however,  a 
statistical  study  to  quantify  the  reliability  of  this  technique  has  not  (to  my 
knowledge)  been  carried  out.  It  could  provide  the  much  needed  "success  story" 
for  weather  modification.  The  dispersal  of  warm  fogs  is  a  much  more  difficult 
problem  which  has  not  yielded  to  subtle  approaches.  The  U.S.  Air  Force  has 
concluded  that  the  best  approach  to  this  problem  is  through  direct  heat  input ;  this 
approach  appears  sufficiently  promising  that  it  should  be  subjected  to  proper 
physical  and  statistical  evaluation.  The  possibility  of  targeting  winter  orographic 
snowfall  to  specific  areas  on  the  ground  (e.g.,  reservoirs)  has  been  investigated. 
.  .  .  The  technique  shows  sufficient  promise  that  further  studies  involving  both 
physical  and  statistical  evaluation  should  be  carried  out.  Attempts  at  modifying 
the  precipitation  from  cumulus  clouds  dates  back  to  the  beginning  of  modern 
weather  modification  (the  1940's)  ;  however,  very  few  of  these  projects  have 
involved  both  physical  and  statistical  evaluation  (and  many  have  used  neither). 

12  Changrnon,  Stanley  A.,  Jr.,  "Present  and  Future  of  Weather  Modification;  Regional 
Issues,"  1975.  pp.  172-174. 

13  Ibid.,  p.  172. 


In  view  of  our  growing  understanding  of  the  structure  and  life  cycles  of  individual 
cumulus  clouds,  and  the  auvances  which  have  been  made  in  the  numerical 
simulation  of  these  processes,  the  time  is  now  ripe  to  mount  a  substantial  investi- 
gation to  determine  whether  precipitation  from  these  clouds  can  be  increased. 

The  primary  components  of  the  comprehensive  research  projects  recommended 
above  should  be  physical,  statistical,  and  theoretical  analysis.  Physical  evalua- 
tions should  include  comprehensive  field  studies  using  a  wide  range  of  airborne, 
ground,  and  remote  probing  techniques  to  evaluate  the  natural  systems  and  the 
degrees  to  which  they  can  oe  artificially  modified.  Physical  testing  and  evaluation 
of  a  proposed  weather  modification  technique  is  best  commenced  prior  to  the 
establishment  of  a  statistical  design,  for  not  only  can  physical  evaluations  check 
the  feasibility  of  a  proposed  technique,  but  they  can  indicate  the  conditions  under 
which  it  is  most  likely  to  be  effective  and  thereby  aid  in  sharpening  or  the 
statistical  design.  A  sound  weather  modification  technique  should  also  be  based 
on,  or  supported  by,  the  best  theoretical  models  available  for  describing  the 
weather  system  under  investigation.  If  the  theoretical  and  physical  studies 
indicate  that  a  particular  weather  modification  technique  is  effective,  a  carefully 
designed  randomized  statistical  experiment  should  follow.  Theoretical  and 
physical  evaluations  should  continue  through  the  statistical  experiment.  An 
independent  repetition  of  the  experiment  in  at  least  one  other  geo  raphieal 
area  will  generally  be  required.  The  confluence  of  results  from  theoretical,  phys- 
ical, and  statistical  analyses  carried  out  in  two  areas  would  permit  sound 
quantitative  evaluation  of  the  effectiveness  of  an  artificial  modification 


In  the  1973  study  published  by  the  National  Academy  of  Sciences  15 
three  broad  research  goals  for  weather  modification  were  recommended 
along  with  specific  research  programs  and  projects  required  to  achieve 
those  goals.  The  three  goals  are : 

1.  Identification  by  the  year  1980  of  the  conditions  under  which 
precipitation  can  be  increased,  decreased,  and  redistributed  in 
various  climatological  areas  through  the  addition  of  artificial  ice 
and  condensation  nuclei ; 

2.  Development  in  the  next  decade  of  technology  directed 
toward  mitigating  the  effects  of  the  following  weather  hazards : 
hurricanes,  hailstorms,  fogs,  and  lightning ;  and 

3.  Establishment  of  a  coordinated  national  and  international 
system  for  investigating  the  inadvertent  effects  of  manmade  pol- 
lutants, with  a  target  date  of  1980  for  the  determination  of  the 
extent,  trend,  and  magnitude  of  the  effect  of  various  crucial  pol- 
lutants on  local  weather  conditions  and  on  the  climate  of  the 

Achievement  of  these  national  goals  would  require,  according  to 
the  National  Academy  study,  implementation  of  the  following  research 
efforts,  some  in  support  of  all  three  goals  and  others  as  a  means  to 
achieving  each  of  the  three  goals : 
A.  Recommended  research  in  support  of  all  three  goals : 

1.  More  adequate  laboratory  and  experimental  field  programs 
are  needed  to  study  the  microphysical  processes  associated  with 
the  development  of  clouds,  precipitation,  and  thunderstorm 

14  Hohhs.  "Weather  Modification  ;"  a  Brief  Review  of  the  Current  Status  and  Suggestions 
for  Future  Research,"  1977,  pp.  12-13. 

15  Nnt'onal  Academy  of  Sciences,  "Weather  and  Climate  Modification  ;  Problems  and  Prog- 
ress," 1973. 

"  Ibid.,  p.  27. 


2.  There  is  a  need  to  develop  numerical  models  to  describe  the 
behavior  of  layer  clouds,  synoptic  storms,  orographic  clouds,  and 
severe  local  clouds. 

3.  There  is  a  need  for  the  standardization  of  instrumentation  in 
seeding  devices  and  the  testing  of  new  seeding  agents. 

4.  There  should  be  established  a  number  of  weather  modifica- 
tion statistical  research  groups  associated  with  the  major  field 
groups  concerned  with  weather  modification  and  the  inadvertent 
effects  of  pollutants. 

5.  There  should  be  created  a  repository  for  data  on  weather 
modification  activities,  and,  at  a  reasonable  price,  such  data  should 
be  made  available  for  reanaiyses  of  these  activities. 

B.  Recommended  research  in  support  of  goal  1  above : 

1.  There  is  a  continuing  need  for  a  comprehensive  series  of 
randomized  experiments  to  determine  the  effects  of  both  artificial 
and  natural  ice  and  cloud  nuclei  on  precipitation  in  the  principal 
meteorological  regimes  in  the  United  States. 

2.  Investigations  into  the  feasibility  of  redistributing  winter 
precipitation  should  be  continued  and  expanded. 

3.  Experiments  need  to  be  designed  so  that  the  effects  of  seeding 
on  precipitation  outside  the  primary  area  of  interest  can  be 

4.  Studies  of  the  effects  of  artificial  seeding  on  cumulus  clouds 
and  the  numerical  modeling  of  the  seeding  process  should  be  con- 
tinued and  expanded. 

C.  Recommended  research  in  support  of  goal  2  above : 

1.  Investigations  should  be  made  to  determine  whether  the  seed- 
ing techniques  presently  used  in  the  study  of  isolated  cumlus 
clouds  and  in  hurricane  modification  can  be  extended  to,  or  new 
techniques  developed  for,  the  amelioration  of  severe  thunder- 
storms, hailstorms,  and  even  tornadoes. 

2.  An  expanded  program  is  needed  to  provide  continuous  birth- 
to-death  observations  of  hurricanes  from  above,  around,  within, 
and  beneath  seeded  and  nonseeded  hurricanes  and  for  testing  of 
existing  and  new  techniques  for  reducing  hurricane  intensities. 

3.  Studies  on  the  development  of  hurricane-modification  tech- 
niques should  include  a  randomization  scheme  in  the  design  and 
conduct  of  experimental  programs. 

4.  A  major  national  effort  in  fundamental  research  on  hailstorms 
and  hailstorm  modification  should  be  pursued  aggressively. 

5.  A  comprehensive  program  dealing  with  research  on  warm 
fog  and  its  dissipation  should  be  undertaken. 

6.  A  high  priority  should  be  given  to  the  development  of  a  vari- 
ety of  research  techniques  specifically  designed  for  observing 
severe  storms. 

D.  Recommended  research  in  support  of  goal  3  above : 

1.  National  and  international  programs  should  be  developed 
for  monitoring  the  gaseous  and  particulate  content  of  the  atmos- 
phere, with  particular  emphasis  on  modification  by  man's 

2.  Satellite  programs  should  be  developed  to  monitor  continu- 
ally, on  a  global  basis,  the  cloud  cover,  albedo,  and  the  heat  bal- 
ance of  the  atmosphere. 


3.  There  should  be  enlarged  programs  to  measure  those  para- 
meters that  describe  the  climate  of  cities  and  adjoining  country- 
sides and  to  determine  the  physical  mechanisms  responsible  for 
these  differences. 

4.  Continued  strong  support  should  be  provided  to  the  major 
effort  now  underway,  known  as  the  Global  Atmospheric  Research 
Program,  to  develop  properly  parameterized  mathematical  models 
of  the  global  atmosphere-ocean  system,  to  obtain  the  observational 
data  to  test  their  efficacy,  and  to  provide  the  computers  that  permit 
simulation  of  the  effects  of  human  activities  on  a  worldwide  scale.17 

Some  of  the  recommended  research  activities  discussed  above  were 
already  underway  at  the  time  of  the  1973  National  Academy  study, 
but  continuation  or  expansion  of  these  efforts  were  advised.  Since  that 
time  others  have  been  initiated,  and  beneficial  results  from  continua- 
tion and  expansion  of  earlier  efforts  have  been  achieved.  The  overall 
decrease  in  funding  of  the  Federal  research  program  in  the  past  few 
years  has  resulted  in  curtailments  of  valuable  research  projects  identi- 
fied to  meet  the  goals  above,  however,  and  the  current  level  of  research 
activities  can  hardly  lead  to  achievement  of  the  goals  set  by  the  Acad- 
emy study.  The  recent  history  of  Federal  funding  for  weather  modi- 
fication is  discussed  and  summarized  in  chapter  5,  as  part  of  the  treat- 
ment on  Federal  activities.18 


Concerned  that  its  research  programs  be  more  responsible  to  societal 
needs,  the  Weather  Modification  Project  Office  of  the  National  Oceanic 
and  Atmospheric  Administration  (NOAA)  established  a  small  ad- 
vanced planning  group  in  1976.  Consisting  of  one  full-time  and  three 
part-time  members,  none  of  whom  were  permanent  NOAA  employees, 
the  advanced  planning  group  was  charged  with  making  recommenda- 
tions and  preliminary  plans  for  research  projects  to  be  carried  out 
over  the  following  10  to  15  years.  The  group  set  about  its  task  by 
visiting  various  user  groups  to  learn  opinions  about  past  Federal 
research  and  by  reviewing  available  literature  and  consulting  scien- 
tists on  past  and  current  weather  modification  field  programs.19 

The  advanced  planning  group  acknowledged  that  considerable  prog- 
ress had  been  made  in  weather  modification  in  the  past  few  years, 
but  noted  that  the  current  research  approach  has  the  following  short- 
comings : 

1.  Research  in  the  United  States  on  stimulation  of  precipitation 
has  been  concentrated  in  the  semiarid  western  States  and  in  Flor- 
ida rather  than  in  the  Corn  Belt,  where  the  potential  economic 
payoff  is  much  greater. 

2.  Research  on  stimulation  of  rainfall  and  on  suppression  of 
hail  and  lightning  have  been  carried  out  in  separate  projects.  A 
single  project  dedicated  to  the  concept  of  precipitation  manage- 
ment in  large  convective  clouds  would  be  more  likely  to  solve  the 
problem  of  changing  hailfall  and  rainfall  simultaneously  to  pro- 
duce net  economic  benefits. 

»  Ibid.,  pp.  27-30. 

18  Sop  n  242. 

w  Dennis  Arnott  S.  and  A.  Gaprln.  "Rocommendat'ons  for  Future  Research  in  Weather 
Modification,"  Weather  Modification  Program  Office.  Environmental  Research  T.aboartories, 
Nntionm  Ocennic  nnr]  Atmospheric  Administration,  U.S.  Department  of  Commerce,  Bouldei* 
Colo.,  November  1977,  112  pp. 


3.  Weather  modification  has  usually  been  equated  with  cloud 
seeding.  Other  possible  means  of  modifying  the  weather  have 
been  largely  ignored. 

4.  Weather  modification  is  usually  considered  in  isolation, 
rather  than  as  an  integral  part  of  a  total  response  to  weather- 
related  problems.  There  are  exceptions :  dry  ice  seeding  to  improve 
visibility  during  cold- fog  episodes  at  airports  is  normally  viewed 
as  a  supplement  to,  rather  than  a  replacement  for,  good  instru- 
ment landing  systems.  However,  cloud  seeding  to  increase  pre- 
cipitation is  sometimes  viewed  as  an  alternative  to  irrigation  or 
water  conservation  measures,  a  situation  we  think  is  regrettable. 
Fortunately,  research  in  inadvertent  weather  modification  is  tend- 
ing to  break  down  the  artificial  isolation  of  research  related  to 
weather  modification  from  other  aspects  of  atmospheric  science.20 

Having  examined  the  current  weather  modification  research  situa- 
tion as  perceived  by  user  groups  and  research  scientists,  the  NOAA 
Advanced  Planning  Group  proceeded  to  formulate  recommendations 
for  future  research,  using  certain  general  technical,  economic  and  soci- 
ological guidelines.  Proposed  research  was  evaluated  on  the  basis  of 
answers  to  the  following  questions : 

1.  Will  the  project  advance  scientific  understanding  of  atmos- 
pheric processes  and  thereby  contribute  to  an  improved  capability 
to  modify  weather  on  a  predictable  basis  ? 

2.  Will  the  operational  capability  toward  which  the  project  is 
directed  provide  net  economic  benefit? 

3.  Are  the  proposed  research  and  the  possible  subsequent  appli- 
cations socially  acceptable  % 21 

The  group  completed  its  study  during  1977  and  provided  its  recom- 
mended research  program  to  NOAA's  Weather  Modification  Project 
Office.  The  5  specific  recommendations  are  summarized  below : 

1.  Work  should  be  continued  to  determine  the  potential  for  in- 
creasing rainfall  from  convective  clouds  in  warm,  humid  air 
masses  by  seeding  for  dynamic  effects.  Design  of  a  new,  compre- 
hensive project  to  be  conducted  in  the  eastern  half  of  the  United 
States  should  begin  immediately.  This  project  should  gather  in- 
formation on  the  effects  of  seeding  upon  rainfall,  hail,  lightning, 
and  thunderstorm  winds  both  within  and  outside  a  fixed  target 
area.  Additional  field  studies  in  Florida  to  establish  the  physical 
mechanisms  responsible  for  the  apparent  increases  in  total  target 
rainfall  during  FACE  22  in  1975-76  should  be  performed  during 
at  least  two  seasons  in  parallel  with  the  design  of  the  new  project. 
The  results  of  the  additional  studies  would  be  valuable  input  for 
the  design  of  the  new  comprehensive  experiment. 

2.  Because  of  the  promising  beginnings  of  the  Sierra  Coopera- 
tive Project  on  orographic  precipitation  and  the  HIPLEX  23  work 
on  cumulus  clouds  in  the  semiarid  western  States,  and  because  the 
projects  are  likely  to  produce  important  results  of  wide  applica- 

20  Ibid.,  p.  8. 
a  Ibid.,  pp.  8-9. 

22 The  Florida  Area  Cumulus  Experiment  (FACE),  an  experimental  project  sponsored  by 
NOAA's  discussed  under  activities  of  the  U.S.  Department  of  Commerce  in  ch.  5.  p.  292. 

23  The  Sierra  Cooperative  Project  and  the  High  Plains  Cooperative  Program  (HIPLEX) 
are  projects  sponsored  under  the  Division  of  Atmospheric  Water  Resources  Management  of 
the  Bureau  of  Reclamation  in  the  U.S.  Department  of  the  Interior.  These  projects  are  dis- 
cussed in  ch.  5,  pp.  258  and  263,  respectively. 


tion,  we  see  no  reason  for  new  initiatives  in  these  areas  until  those 
projects  are  completed. 

3.  In  view  of  the  need  for  more  detailed  knowledge  of  hurricane 
behavior,  we  recommend  that  research  on  hurricane  modification 
be  continued  with  the  understanding  that  the  research  is  a  long- 
term  effort  with  potenial  payoff  10  to  20  years  away.  We  recom- 
mend further  that  modeling  and  other  theoretical  work  be  intensi- 
fied to  provide  a  better  basis  for  interpretation  of  data  from 
seeding  trials. 

4.  Concepts  for  hail  suppression  and  lightning  suppression 
should  be  subjected  to  fundamental  reappraisal  before  the  resump- 
tion of  any  field  experiments. 

5.  Long-range  planning  should  be  continued  toward  "futuristic" 
projects  in  which  problems  in  deliberate,  large-scale  weather  mod- 
ification, inadvertent  weather  modification,  forecasting,  and  agri- 
cultural climatology  would  be  treated  together  rather  than 


At  the  request  of  NOAA's  Advanced  Planning  Group,  whose  study 
was  discussed  in  the  previous  section,  the  North  American  Interstate 
Weather  Modification  Council  (NAIWMC)  25  compiled  information 
on  recommended  Federal  weather  modification  research,  based  on  the 
needs  of  users  within  NAIWMC  member  States.  Opinions  of  State  offi- 
cials on  needed  research  were  obtained  from  16  States  through  meet- 
ings sponsored  by  California,  North  Dakota,  Pennsylvania,  South  Da- 
kota. Texas,  and  Utah  and  through  questionnaires  sent  out  by  the 
NAIWMC  during  1976  and  1977. 

Table  14  summarizes  results  of  the  NAIWMC  investigation,  showing 
perceived  needs  for  research  for  weather  modification  users,  as  inter- 
preted by  the  State  officials.26  Keyes  notes  that  the  major  research  area 
recommended  by  most  State  and  local  governments  is  in  the  evalua- 
tion of  ongoing,  long-term  operational  projects  within  those  States. 
Other  important  research  needs  expressed  were  for  further  develop- 
ment of  seeding  technology  and  for  economic,  environmental,  and 
societal  studies  necessary  for  eventual  public  acceptance  of  weather 

15  The  purposes,  organization,  and  activities  of  the  North  American  Interstate  Weather 
Modification  Council  are  discussed  in  some  detail  in  ch.  7.  p.  333. 

26  Reves.  Conrad  G..  Jr..  "Federal  Research  Needs  and  New  Law  Requirements  in  Weather 
Modification  :  the  NAIWMC  Viewpoint,"  testimony  before  the  U.S.  Department  of  Commerce 
We.ither  Modification  Advisory  Board,  Champaign,  111.,  Oct.  14.  1977. 

»  Ibid. 



[From  Keyes,  1977;  table  format  from  Dennis  and  Gagin,  1977] 

Major  categories  of  research  i 


Arizona   a,  b,  c  a,  b,  e...  a,  b,  c  

California   a,  b,  c  a,  b  a,  b,  c  

Illinois   a,  b,  c  a,  b,  c,  d.  a,  b,  c  Yes  

Indiana   b,  c  a,  b,  c,  e.  b,  c  Yes  

Kansas   a,  b,  c  b,  c  a,  c  

Maryland   a,  b,  c       b,  c  Yes  Yes. 

Michigan   a,  b,  c  b,  c  a  Yes  

Missouri   a,  b  a,  c  

North  Carolina  2  

North  Dakota   a  b,  c,  e  c  a. 

Pennsylvania   c  c  Yes  Yes  

South  Dakota   a,  b,  c  b,  c  c  

Texas   a,  c  a,  b,  d...  c  a,  c. 

Utah   a,  b  b,  d  a  

Vermont   a  a  a  a,  c. 

Virginia s  

•  Categories  of  Federal  research: 

1.  Evaluation: 

a.  Of  operational  programs. 

b.  Physical  studies. 

c.  Extra-area  effects. 

2.  Seeding  technology: 

a.  New  seeding  agents. 

b.  Transport  and  diffusion,  delivery  methods. 

c.  Hail  suppression  methods. 

d.  New  tools,  for  example,  satellites. 

e.  Public  education. 

3.  Economic,  ecological,  and  societal  studies: 

a.  Economic  benefits. 

b.  Toxicity  of  agents. 

c.  Societal  studies. 

4.  Detection  of  clandestine  seeding. 

5.  Inadvertent  weather  modification. 

6.  Forecasting: 

a.  Short  range. 

b.  Local  topographic  effects. 

c.  Long  range. 

3  Need  a  national  policy  first. 
3  Mainly  hurricane  modification. 



Recently,  the  chairman  of  the  Committee  on  Weather  Modifica- 
tion of  the  American  Meteorological  Society  28  summarized  his  com- 
mittee's recommendations  on  recommended  weather  modification  re- 
search needs.29  It  was  noted  that  the  primary  focus  of  such  research 
should  be  in  the  areas  of  purposeful  alteration  of  patterns  of  cloud 
systems  and  precipitation  and  in  the  inadvertent  impact  of  man's 
activities.  In  view  of  critical  water  problems  affecting  large  portions 
of  the  country  and  the  potential  for  increased  demand  for  application 
of  weather  modification  techniques  by  water  users,  the  necessity  for 
improved  understanding  of  underlying  physical  processes  through 
pursuit  of  basic  research  was  emphasized.  In  particular,  the  "real 
payoff"  to  improvements  in  purposeful  weather  modification  should 
be  seen  as  coming  from  increased  ability  to  understand,  predict,  and 

28  Weather  modification  activities  of  the  American  Meteorological  Society  and  purposes 
and  concerns  of  its  Committee  on  Weather  Modification  are  discussed  in  ch.  8,  p.  395. 

29  Silverman.  Bernard  A.,  testimonv  before  the  U.S.  Department  of  Commerce  Weather 
Modification  Advisory  Board,  Champaign,  111..  Oct.  14.  1977. 


control  the  formation  and  development  of  mesoscale 30  cloud  systems.31 

Subject  areas  for  recommended  research  to  accomplish  basic  under- 
standing of  atmospheric  processes  necessary  for  the  development  of 
weather  modification  technology  were  presented  by  the  AMS  com- 
mittee in  the  following  outline  form : 32 

M esoscale  Cloud  Dynamics 

A.  Effect  of  seeding  on  convective  cloud  development  and 
evolution  : 

1.  Growth  of  convective  clouds. 

2.  Merger  of  clouds  into  groups  and  systems. 

3.  Organization  of  inflow  (coupling  of  midtroposphere  with 
the  boundary  layer). 

4.  Enhanced  moisture  budget  efficiency. 

B.  Interaction  of  clouds  with  each  other  and  with  their  environ- 
ment : 

1.  Response  to  mesoscale  forcing  function. 

2.  Relationship  between  low-level  convergence  and  cloud  field 

3.  Role  of  outdrafts  in  development  and  sustenance  of  cloud 

4.  Role  of  anvils  in  the  evolution  of  the  cloud  field. 

C.  Precipitation  "nowcasting" : 

1.  Low-level  convergence  field  as  predictor  of  precipitation 

2.  Kinematic  and  thermodynamic  predictors  and  covariates  for 
statistical  evaluation. 

D.  Need  for  a  multidisciplined  mesoscale  experiment  with  strong 
physical  emphasis. 

Precip  itation  Microp  hysics 

A.  Evolution  of  natural  ice  in  cloud : 

1.  Nucleation  processes. 

2.  Secondary  ice  production  processes  : 

(a)  Laboratory  studies  of  causality. 

(b)  Field  investigations  to  define'  appropriate  in-cloud 
criteria  for  multiplication  of  ice. 

B.  Interaction  between  microphysics  and  dynamics  to  produce  and 
sustain  precipitation. 

C.  Effect  of  seeding  on  (A)  and  (B)  above. 

D.  Distinction  between  microstructure  of  clouds  developing  over 
land  and  over  water  in  terms  of  suitability  for  seeding. 

E.  Clarification  of  microstructure  of  clouds  developing  within  the 
hurricane  environment  in  terms  of  suitability  for  seeding. 

F.  Cloud  microstructure  climatology  for  selected  regions  of  the 
United  States. 

G.  Effect  of  ice  generation  on  charge  separation  and  electrification 

30  Mpsosealo  meteorological  phenomena  are  those  with  horizontal  dimensions  ranging  from 
a  few  tens  of  kilometers  to  a  few  hundred  kilometers. 

a  Silverman,  testimony  before  Weather  Modification  Advisory  Board,  1977. 
»  Ibid. 


Area  of  Seeding  Effect 

A.  Induced  by  dynamic  response  of  environment. 

B.  Induced  by  diffusion  of  nucleating  material : 

1.  In  orographic  regions. 

2.  Transport  through  convective  processes. 

C.  Insolation  pattern  resulting  from  mid-  and  upper-level  outflow. 

Turbulence  and  Diffusion 

A.  Targeting  of  surface-based  source (s)  of  nuclei  into  desired  cloud 

B.  Entrainment  processes  related  to  cloud  development. 

C.  Spread  of  nuclei  released  in  cloud  (spatial  and  temporal 

Seeding  Agents  and  Methods 

A.  Nucleation  efficiency  studies. 

B.  Particle  sizing  and  composition  analyses. 

C.  Particle  generation  systems. 

D.  Improvement  of  technology. 

Cloud  Climatology  for  Technology  Applicability 

A.  National  in  scope. 

B.  Frequency  of  occurrence  of  clouds  by  type. 

C.  Cloud  base  and  cloud  top  heights  for  selected  regions. 

D.  Properties  of  in-cloud  microstructure. 

E.  Aerosol  characteristics. 

F.  Radar  population  studies. 

G.  Precipitation  statistics. 

H.  Model-derived  "seedability"  assessment. 

Inadvertent  Impacts 

A.  Effect  on  climatic  change. 

B.  Effect  on  air  quality. 

,C.  Effect  on  meteorology  near  large  urban  regions : 

1.  Thermal  pattern. 

2.  Precipitation. 

3.  Cloudiness. 

D.  Effect  on  meteorology  near  deforested  areas. 

Cloud  M  odeling 

A.  Synthesis  of  numerical  simulation  with  atmospheric  observations 
on  all  scales. 

B.  Inclusion  of  cloud  interaction  and  outdraft  convergence. 

C.  Mesoscale  forcing  (e.g.  sea  breeze,  topography,  etc.). 

Improved  Methods  of  Statistical  Design  and  Evaluation 

A.  Required  to  interpret  results  of  new  mesoscale  experiment. 

B.  Required  for  extraction  of  physical  information  from  previously- 
performed  nonrandomized  experiments. 

34-857  O  -  79  -  12 


Study  of  oak  brush  as  elk  forage — part  of  environmental  research  conducted 
part  of  Project  Skywater.  (Courtesy  of  the  Bureau  of  Reclamation.) 




At  the  1977  workshop  on  the  extended  area  and  extended  time  ef- 
fects of  weather  modification,  participants  developed  some  recommen- 
dations for  future  research  into  these  effects.33  The  following  research 
activities,  not  necessarily  in  any  order  of  priority,  were  recommended 
to  be  undertaken  immediately  with  current  available  tools  or  over  a 
period  of  time,  as  appropriate : 

The  use  of  computer  simulation  and  modeling  can  provide 
important  information  on  the  areal  coverage  and  magnitude  of  the 
effects  of  weather  modification.  It  can  also  define  the  types  of  in- 
formation and  the  sensitivity  required  for  future  field 

Models  developed  to  detect  moisture  depletion  in  natural  and 
seeded  cases  as  an  airmass  moves  over  successive  mountain  ridges 
should  be  applied  and  verified  by  field  measurements  in  an  area 
with  a  minimum  of  complexities  caused  by  the  introduction  of  new 
moisture  sources.  In  situ  measurements  of  temperature,  pressure, 
liquid  water  content,  ice  crystal  concentrations,  and  precipitation 
on  the  ground  and  in  the  air  will  be  needed  as  inputs  to  the  model 
and  for  model  validation. 

An  intensive  study  should  be  initiated  on  particulate  transport, 
including  the  transport  of  both  seeding  material  and  ice  crystals 
produced  by  seeding.  Techniques  are  currently  available  to 
measure  ice  crystal  concentrations,  nuclei,  and  silver  in  precipi- 
tation. Special  tracers  are  becoming  available  and  should  be  de- 
veloped further.  Eemote  sensing  techniques  for  measuring  ice  and 
water  need  further  development. 

A  re-analysis  of  some  past  field  programs  could  be  undertaken 
immediately.  (The  question  of  apparent  decreases  in  seeding  ef- 
fectiveness in  successive  years  of  the  Australian  experiment  has 
not  been  resolved  adequately  as  to  whether  this  effect  is  real  or  an 
analysis  artifact.  The  reported  persistence  of  ice  nuclei  for  days 
after  seeding  at  Climax  and  its  relationship  to  the  apparent 
decrease  in  the  seed/no  seed  ratios  with  time  should  be  further 

Continuing  monitoring  should  be  initiated  of  such  quantities 
as  ice  nuclei  concentrations  in  project  areas  in  order  to  establish 
new  benchmarks.  A  modeling  effort  should  also  be  undertaken  to 
investigate  the  evaporation  and  reprecipitation  processes. 

Studies  of  wide-area  effects  from  seeding  summer  convective 
storm  systems  may  require  more  preliminary  work  before  mount- 
ing a  major  field  effort  since  less  is  known  about  these  phenomena. 
These  studies  should  be  directed  toward  acquiring  information 
about  the  possible  redistribution  of  convective  instability  and  the 
microphysical  effects  including  the  transport  of  ice  nuclei  and/ or 
ice  crystals,  and  the  possible  interactive  effects  when  these  par- 
ticles are  entrained  into  other  cloud  systems. 

Prior  to  the  design  of  a  major  wide-area  study  program,  initial 
studies  should  include :  cloud  population  studies,  including  time 

33  Brown,  et  al..  "Transactions  of  the  Workshop  on  Extended  Space  and  Time  Effects  of 
Weather  Modification,"  1978,  pp.  14-18. 


and  space  distributions  and  cloud  microphysics ;  hypothesis  de- 
velopment, including  numerical  modeling ;  reexamination  of  pre- 
vious experimental  programs ;  augmentation  of  ongoing  programs 
to  study  total-area  effects;  and  development  of  new  capabilities 
including  satellite  measurements,  rain  gage  network  design,  data 
processing,  and  management  and  seeding  delivery  systems. 

The  final  design  of  a  field  program  will  be  dependent  on  the 
findings  from  these  preliminary  studies.  It  appears  likely  that  it 
will  be  necessary  to  mount  a  major  effort  to  determine  the  total- 
area  effects  and  mechanics  of  convective  storm  seeding.  Prelimi- 
nary estimates  call  for  a  10-year  studv  covering  nn  area  of  at  least 
a  300-mile  radius  in  the  mid-United  States.  Ideally  this  study 
could  be  operated  in  conjunction  with  other  mesoscale  field  studies 
in  cumulus  convection  and  precipitation  forecasting. 

A  national  technology  assessment  on  precipitation  modification 
should  be  conducted  with  the  total-area  effect  included  in  both 
the  physical  science  and  social  science  context.34 

a*  Ibid. 



(By  John  R.  Justus,  Analyst  in  Earth  Science,  Science  Policy  Research  Division, 
Congressional  Research  Service) 

Out  of  the  total  ensemble  of  environmental  factors,  the  subset  which 
is  sensed  most  immediately  and  directly  by  man  and  which  has  the 
greatest  integrated  impact  on  human  activities  is  that  which  is  sub- 
sumed under  the  terms  of  iveather  and  climate. — Earl  W.  Barrett, 
1975,  National  Oceanic  and  Atmospheric  Administration. 


The  relationship  between  man  and  weather  has  been  basically  the 
one  stated  succinctly  by  Charles  Dudley  Warner:  Everybody  talked 
about  the  weather,  but  nobody  did  anything  about  it.  In  the  1940's, 
however,  the  discovery  that  clouds  could  be  modified  by  additions  of 
freezing  nuclei  created  a  realization  that,  at  some  times  and  places  at 
least,  it  might  be  possible  to  do  something  about  the  weather.  This 
entering  wedge  into  the  field  of  intentional  or  planned  weather  modi- 
fication has  since  been  heavily  studied  and  exploited ;  it  had,  as  a  by- 
product, the  creation  of  considerable  interest  in  weather  modification 
on  the  part  of  both  the  scientific  community  and  the  general  popula- 
tion. The  science  and  technology  of  planned  weather  modification  are' 
discussed  in  chapter  3.  The  possibility  that  man  has,  in  fact,  been  doing 
something  about  the  weather  without  knowing  it  has  become  a  subject 
for  serious  consideration,  and  chapter  4  reviews  a  number  of  processes 
and  mechanisms  governing  inadvertent  weather  and  climate  modifi- 


By  way  of  clarification,  it  is  important  to  appreciate  the  fact  that 
differences  of  scale  are  implied  in  the  terms  "weather  modification" 
and  "climate  modification." 


To  most  everyone,  the  term  climate  usually  brings  to  mind  an  aver- 
age regime  of  weather  or  the  average  temperature  and  precipitation 
of  a  locality.  This  is  a  rather  misleading  concept,  for  the  average  may 
be  a  rare  event.  Actually,  weather  from  year  to  year  oscillates  widely 
so  that  climate  is  a  statistical  complex  of  many  values  and  variables, 
including  the  temperature  of  the  air,  water,  ice,  and  land  surfaces; 
winds  and  ocean  currents ;  the  air's  moisture  or  humidity ;  the  cloudi- 
ness and  cloud  water  content,  groundwater,  lake  levels,  and  the  water 
content  of  snow  and  of  land  and  sea  ice;  the  pressure  and  density  of 



the  atmosphere  and  ocean;  the  composition  of  (dry)  air;  and  the 
salinity  of  the  ocean.  All  of  these  elements  encompass  climate  and  are 
interconnected  by  the  various  physical  and  dynamic  processes  occur- 
ring in  the  system,  such  as  precipitation  and  evaporation,  radiation, 
and  the  transfer  of  heat  and  momentum  by  advection  (predominantly 
horizontal,  large-scale  motions  of  the  atmosphere),  convection  (large- 
scale  vertical  motions  of  the  atmosphere  characterized  by  rising  and 
sinking  air  movements),  and  turbulence  (a  state  of  atmospheric  flow 
typified  by  irregular,  random  air  movements) . 

Climatic  fluctuation  and  climatic  change 

Rather  than  by  average  value,  these  elements  are  best  characterized 
by  frequency  distributions,  which  can,  in  many  places,  span  a  wide 
range  for  a  given  element.  Within  such  a  range,  one  notes  irregular 
fluctuations  characterized  by  the  occurrence  of  extreme  values  for  given 
elements  of  the  climatic  system.  In  such  instances,  a  climatic  fluctua- 
tion is  said  to  be  experienced,  not  a  climatic  change.  A  change  denotes 
that  a  new  equilibrium  had  been  achieved,  and  with  it,  a  rather  dif- 
ferent frequency  distribution  for  all  climatic  elements.  Thus,  the  term 
change  is  not  to  be  confused  with  fluctuation,  where  trends  are  fre- 
quently reversed,  even  though  some  successive  values  may  cluster  for 
a  while  on  one  side  or  the  other  of  the  "average." 


Defined  as  the  state  of  the  atmosphere  at  any  given  time,  the  prev- 
alent belief  of  the  public,  that  wherever  the  weather  goes  the  climate 
follows,  is  fallacious.  On  the  contrary,  wherever  the  climate  goes,  so 
goes  the  weather.  Weather  is  merely  a  statistic  of  the  physical  climatic 

Weather  modification 

As  used  in  the  context  of  this  chapter  and  in  the  text  at  large, 
weather  modification  refers  collectively  to  any  number  of  activities 
conducted  to  intentionally  or  inadvertently  modify,  through  artificial 
means,  the  elements  of  weather  and,  in  turn,  the  occurrence  and  be- 
havior of  discrete  weather  events.  Intentional  or  planned  weather 
modification  activities  may  be  conducted  for  a  variety  of  different 
purposes,  including:  Increasing  or  decreasing  rain  and  snow  over  a 
particular  area;  reducing  damage  to  crops  and  property  from  hail; 
reducing  the  number  of  forest  fires  that  are  started  by  lightning; 
removing  fog  at  airports;  changing  the  intensity  and  direction  of 
hurricanes  so  they  cause  less  destruction ;  mitigating  the  destructive- 
ness  of  severe  thunderstorms  and  tornadoes. 

Climate  modification 

This  encompasses  the  planned  or  inadvertent  alteration,  through 
artificial  means,  of  the  elemental  properties  comprising  the  air,  sea,  ice, 
land,  and  biospheric  components  of  the  climatic  system  in  order  to 
effect  a  new  equilibrium  among  the  elements  of  climate  and,  conse- 
quently, a  new  climate  regime.  In  most  instances,  the  term  alludes  to 
mesoscale  and  macroscale  climates,  from  those  of  regions  to  the  entire 
globe.  Another  common  usage  is  in  reference  to  the  microscale  climates 
of  cities  where  persistent,  inadvertent  effects  on  weather,  in  turn, 
modify  the  climates  of  greater  metropolitan  areas. 


Planned  climate  modification 

While  the  term  climate  usually  brings  to  mind  an  "average"  regime 
of  weather  or,  more  properly,  a  frequency  distribution  of  the  elements 
and  events  of  weather,  the  climatic  system  itself  consists  of  those 
elements  and  processes  that  are  basically  the  same  as  those  responsible 
for  short-term  weather  and  coordinately  for  the  maintenance  of  the 
long-term  physical  climatic  state.  It  follows,  then,  that  one  of  the  pur- 
poses of  planned  weather  modification  activities  may  be  to  artificially 
change  the  climate  of  a  location  or  region  through  means  including, 
but  not  necessarily  limited  to:  Massive  and  protracted  extension  of 
present  cloud-seeding  operations  to  influence  natural  precipitation  de- 
velopment cycles;  intentional  initiation  of  large  heat  sources  to  influ- 
ence convective  circulation  or  evaporate  fog ;  intentional  modification 
of  solar  radiation  exchange  or  heat  balance  of  the  Earth  or  clouds 
through  the  release  of  gases,  dusts,  liquids,  or  aerosols  in  the  atmos- 
phere; planned  modification  of  the  energy  transfer  characteristics  of 
the  Earth's  land  or  water  surface  by  dusting  with  powders,  liquid 
sprays  or  dyes,  water  impoundment,  deforestation,  etc. 

The  dramatic  idea  of  some  great  technological  leap  toward  purpose- 
fully altering  climate  never  seems  to  lose  its  appeal.  The  problem  with 
these  grand  schemes  is  that,  even  if  feasible,  every  fix — technological 
or  otherwise — has  its  toll  in  side  effects.  But  leaving  aside  for  the 
moment  the  question  of  whether  it  makes  sense  to  alter  or  conserve 
climate,  many  of  the  schemes  that  have  been  suggested  for  modifying 
climate  on  a  hemispheric  or  global  scale  have  so  far  been  considered  to 
be  on  the  fringe  of  science  fiction.  The  range  of  possibilities  widens 
rapidly  if  one  imagines  the  financial  resources  of  the  major  world 
powers  available  to  carry  them  out.  Periodically  resurgent  are  such 
schemes  as  darkening,  heating,  and  melting  of  the  Arctic  icepack,  the 
damming  of  the  Bering  Strait,  the  transportation  of  Antarctic  ice- 
bergs, the  diverting  southward  of  North  American  and  Asian  rivers 
that  empty  into  the  Arctic,  and  the  modification  of  tropical  storms.1 
These  and  other  perennial  suggestions  are  summarized  in  Figure  1. 

iKellogjr.  W.  W.  and  S.  H.  Schneider,  "Climate  Stabilization:  For  Better  or  for  Worse?" 
Science,  vol.  186,  Dec.  27,  1974,  pp.  1163-1172. 


Figube  1. — A  survey  of  grandiose  schemes  that  have  been  proposed  to  modify  or 
control  climate.  (From  Kellogg  and  Schneider,  1974.) 

Inadvertent  climate  modification 

The  modification  processes  may  also  be  initiated  or  triggered  in- 
advertently rather  than  purposefully,  and  the  possibility  exists  that  so- 
ciety may  be  changing  the  climate  through  its  own  actions  by  pushing 
on  certain  leverage  points.  Inadvertently,  we  are  already  causing 
measurable  variations  on  the  local  scale.  Artificial  climatic  effects  have 
been  observed  and  documented  on  local  and  regional  scales,  partic- 
ularly in  and  downwind  of  heavily  populated  industrial  areas  where 
waste  heat,  particulate  pollution  and  altered  ground  surface  char- 
acteristics are  primarily  responsible  for  the  perceived  climate  modifi- 
cation. The  climate  in  and  near  large  cities,  for  example,  is  warmer, 
the  daily  range  of  temperature  is  less,  and  annual  precipitation  is 
greater  than  if  the  cities  had  never  been  built.  The  climate  of  the  world 
is  governed  mainly  by  the  globally  averaged  effects  of  the  Sun,  the 
location  and  movement  of  air  masses,  and  the  circulation  patterns  of 
the  world  ocean.  It  is  by  no  means  clear  that  the  interaction  of  these 
vast  forces  can  be  significantly  influenced  by  human  activities.  Al- 
though not  verifiable  at  present,  the  time  may  not  be  far  off  when 
human  activities  will  result  in  measurable  large-scale  changes  in 
weather  and  climate  of  more  than  passing  significance.  It  is  important 
to  appreciate  the  fact  that  the  role  of  man  at  this  global  level  is  still 
controversial,  and  existing  models  of  the  general  circulation  are  not  yet 
capable  of  testing  the  effects  in  a  conclusive  manner. 

Nevertheless,  a  growing  fraction  of  current  evidence  does  point  to 
the  possibility  of  unprecedented  impact  on  the  global  climate  by 
human  activities,  albeit  the  effects  may  be  occurring  below  the  thres- 
hold where  they  could  be  statistically  detected  relative  to  the  record 


of  natural  fluctuations  and,  therefore,  could  be  almost  imperceptible 
amid  the  ubiquitous  variability  of  climate.  But  while  the  degree  of  in- 
fluence on  world  climate  may  as  yet  be  too  small  to  detect  against  the 
background  of  natural  variations  and  although  mathematical  models 
of  climatic  change  are  still  imperfect,  significant  global  effects  in  the 
future  are  inferred  if  the  rates  of  growtn  of  industry  and  population 

historical  perspective 

The  possibility  of  climatic  alterations  by  human  activity  was  alluded 
to  in  the  scientific  literature  at  the  beginning  of  this  century,  and  again 
in  the  late  1930's,  but  it  received  little  serious  attention  until  the  1950  s. 
The  first  period  of  thermonuclear  testing,  1954  to  1958,  generated  a 
great  deal  of  concern  about  drastic  and  widespread  elfects  on  weather. 
It  was  felt  that  anything  which  liberated  such  great  energies  must 
somehow  influence  the  atmosphere.  The  fact  that  a  device  fired  at  sea 
level  or  under  the  sea  did  create  locally  a  large  convective  cloud  was 
cited  as  evidence. 

By  about  1960  work  had  shown  that  no  large-scale  or  long-term 
meteorological  effects  would  ensue  from  nuclear  testing  at  the  levels 
conducted  in  the  1950?s.  It  had  become  clear  that  the  inertia  of  the 
atmosphere-ocean  system  was  too  large  to  be  perturbed  seriously  by  the 
sudden  release  of  any  energy  man  could  generate.  Instead  of  the  spec- 
tacular and  violent,  it  was  realized  that  one  would  have  to  look  to  the 
slow  and  insidious  to  find  evidence  of  human  influences  on  climate  and 

Some  evidence  that  manmade  carbon  dioxide  was  accumulating  in 
the  atmosphere  appeared  as  early  as  1938.  This,  together  with  some 
early  systematic  data  from  Scandinavia,  led  to  the  inclusion  of  a  car- 
bon dioxide  (C02)  measurement  program  during  the  International 
Geophysical  Year  (IGY),  1957-1958.  This  C02  measurement  pro- 
gram, which  continues  today,  was  the  first  serious  scientific  study  of 
a  possible  manmade  climatic  influence  on  a  large  scale. 

As  the  reality  of  the  C02  effect  became  established,  and  as  the  gen- 
eral mood  of  increased  concern  for  the  environment  and  the  concept 
of  "spaceship  Earth"  developed  during  the  1960's,  increased  scientific 
efforts  began  to  be  focused  on  inadvertent  weather  and  climate  modi- 
fication. It  had  been  recognized  for  some  time  that  the  climates  of 
cities  differed  significantly  from  their  rural  environs  due  to  the  re- 
lease of  heat  and  pollutants.  It  was  not  until  the  late  1960's  that  evi- 
dence of  "urban  effect"  on  the  climate  at  considerable  distances  down- 
wind began  to  be  noticed.  The  role  of  pollution  aerosols 2  as  climate 
modifiers  became  a  topic  of  great  interest,  and  it  remains  so  today. 

In  the  United  States,  the  attention  of  the  Government  to  these 
problems  began  with  the  IGY  effort,  C02  and  solar  radiation  measure- 
ment programs  were  started  in  Antarctica  and  at  the  Mauna  Loa  Ob- 
servatory in  Hawaii,  which  was  established  specifically  for  this  pro- 
gram by  the  U.S.  Weather  Bureau.  This  station,  located  at  an  eleva- 
tion of  3,400  meters  (11,155  feet)  on  the  north  slope  of  Mauna  Loa, 

2  Dispersions  in  tbe  atmosphere  of  particles  of  matter  that  remain  suspended  for  a  sig- 
nificant length  of  time. 


has  been  improved  over  the  years  and  remains  the  prototype  "bench- 
mark" station  for  climatic  change  monitoring. 

The  first  major  meeting  devoted  exclusively  to  the  inadvertent 
modification  problem  convened  in  Dallas,  Tex.,  in  December  1968.3 

The  following  year,  a  series  of  discussions  between  some  faculty 
members  of  the  Massachusetts  Institute  of  Technology,  government 
officials  and  scientists  gave  rise  to  the  first  working  conference,  the 
Study  of  Critical  Environmental  Problems  (SCEP).  This  meeting, 
held  at  Williams  College,  Wihiamstown,  Mass.,  during  July  1970,  was 
devoted  to  identifying  possible  global  environmental  hazards  and 
making  recommendations  concerning  monitoring,  abatement,  et  cetera. 
The  climatic  problem  areas  identified  were  carbon  dioxide  and  other 
trace  gases  that  may  affect  climate ;  particulate  matter  in  the  atmos- 
phere as  turbidity  and  as  cloud  modifiers ;  waste  heat ;  changes  in  the 
Earth's  surface  (land-use  changes)  ;  radioactivity  in  the  atmosphere; 
and  jet  aircraft  pollution  of  the  high  troposphere  and  stratosphere. 
The  proceedings  of  this  meeting  were  published  by  the  MIT  Press.4' 5 

The  working  group  for  SCEP  was,  with  one  exception,  composed  of 
residents  of  the  United  States :  scientists,  representatives  of  industrial 
management,  and  government  officials.  Some  of  the  participants  felt 
that  a  more  multinational  participation  would  be  essential  if  standard- 
ized global  programs  were  to  come  into  existence  as  a  result  of  such 
a  meeting.  Also,  it  was  the  opinion  that  the  problems  of  climate  modi- 
fication were  complex  enough  to  occupy  the  entire  attention  of  a  work- 
ing meeting.  As  a  result,  a  second  such  meeting  was  held,  this  time  in 
Stockholm,  with  scientists  from  14  countries  participating.  This  work- 
ing meeting  was  called  Study  of  Man's  Impact  on  Climate1  (SMIC). 
The  report  prepared  by  this  group  6  dealt  with  the  substantive  scien- 
tific questions  of  inadvertent  climate  modification,  including:  previous 
climatic  changes;  man's  activities  influencing  climate;  theory  and 
models  of  climatic  change;  climatic  effects  of  manmade  surface 
ciianges;  modification  of  the  troposphere; 7  and  modification  of  the 
stratosphere.8  One  objective  of  SMIC  was  to  provide  guidelines  for 
the  World  Meteorological  Organization  (WMO)  and  other  interna- 
tional agencies  to  use  in  establishing  monitoring  and  research  pro- 
grams on  a  global  scale. 

In  connection  with  the  study  of  inadvertent  climate  modification, 
much  was  iterated  in  the  early  1970's  about  the  need  for  global  moni- 
toring. Because  of  the  lagtime  in  planning,  financing,  and  construct- 
ing such  facilities  (which  must  necessarily  be  in  wilderness  areas  in 
order  to  give  representative  data  not  reflecting  local  effects),  the 
minimum  number  of  benchmark  stations  (10)  considered  necessary 
has  not  yet  been  reached.  Five  stations  are  currently  in  operation. 
Mauna  Loa  Observatory  (MLO),  the  oldest,  was  established  by  the 

3  Singer,  S.  F.,  "Global  Effects  of  Environmental  Pollution,"  New  York.  Springer-Verlag, 

^Wilson  Carroll  L  ,  editor.  Man's  Imnact  on  the  Global  Environment,  Report  of  the 
Study  of  Critical  Environmental  Problems  (SCEP).  Cambridge,  MIT  Press,  1970,  319  pp. 

G  Matthews,  W.  H.,  W.  W.  Kellogg,  and  G.  D.  Robinson,  editors.  "Man's  Impact  on  the 
Climate."  Cambridge,  MIT  Tress.  1971,  r>*)4  pp- 

"Wilson  C  L  and  W  IT  Matthews,  editors,  Inadvertent  Climate  Modification,  Report 
of  the  Study  of  Man's  Impact  on  Climate  (SMIC).  Cambridge,  the  MIT  Press,  1971,  30S  pp. 

7  Troposphere — the  inner  layer  of  the  atmosphere  varying  in  height  from  0  to  12  miles. 
This  is  the  region  within  wMch  nearlv  all  weather  conditions  manifest  themselves. 

8  Stratosphere — the  region  of  the  atmosphere  outside  the  troposphere,  about  10  to  30 
miles  in  height. 


U.S.  Weather  Bureau,  then  transferred  to  the  supervision  of  the 
Atmospheric  Physics  and  Chemistry  .Laboratory  of  the  Environ- 
mental Science  Services  Administration  in  I96ii  and  finally  to  the  Air 
Resources  Laboratory  of  the  National  Oceanic  and  Atmospheric  Ad- 
ministration (NOAA)  in  1971.  In  the  following  year,  the  NOAA  net- 
work was  officially  expanded  to  four  stations:  MLO;  South  Pole; 
Point  Barrow,  Alaska ;  and  American  Samoa.  The  other  operational 
station  is  located  at  Kislovodsk,  North  Caucasus,  in  tne  U.S.S.E.  The 
Government  of  Canada  has  plans  for  three  high  latitude  northern 
stations,  and  some  limited  monitoring  activities  are  conducted  in  Aus- 
tralia and  New  Zealand. 

In  addition  to  the  long-term  monitoring  program,  two  shorter 
programs  have  been  devoted  to  the  inadvertent  modification  problem. 
The  first  of  these,  the  Metropolitan  Meteorological  Experiment 
(Metromex),  was  directed  toward  a  concentrated  investigation  of 
downwind  eiiects  of  the  thermal  and  particulate  emissions  from  a  typi- 
cal metropolitan  area — St.  Louis,  Mo.  The  project  involved  an  exam- 
ination of  all  available  climatological  data  in  a  circle  around  the 
city,  plus  an  extensive  field  program  in  which  a  number  of  State 
and  Federal  Government  agencies  and  university  research  groups 

The  objective  of  the  second  program  was  to  prepare  an  environmen- 
tal impact  statement  on  the  effects  of  supersonic  transport  aircraft. 
The  resulting  research  activity,  the  Climatic  Impact  Assessment  Pro- 
gram (CIAP),  involved  9  agencies  and  departments  of  the  Federal 
Government,  7  agencies  of  other  national  governments,  and  over  1,000 
individual  scientists  in  the  United  States  and  abroad.  The  program 
involved  data-collecting  activities  using  aircraft  and  balloons  in  the 
stratosphere,  development  of  new  techniques  for  sampling  and  measur- 
ing stratospheric  pollutants,  laboratory  work  in  the  photochemistry 
of  atmospheric  trace  gases,  measurement  of  pollutant  emission  by  air- 
craft engines,  mathematical  modeling  of  stratospheric  transport  proc- 
esses and  chemical  reactions  taking  place  there.9 


It  is  a  human  tendency  to  cling  to  the  belief  that  the  natural  environ- 
ment or  climate  to  ivhich  we  have  become  accustomed  will  remain  more 
or  less  the  same  from  year  to  year  and  from  decade  to  decade.  We  are 
surprised  and  alarmed  tohen  an  unusually  severe  winter  or  an  unusu- 
ally prolonged  drought  occurs,  because  our  memories  tend  to  be  too 
short  to  recall  past  years  when  things  were  equally  unusual. 

—William  W.  Kellogg,  1978 
National  Center  for  Atmospheric^  Research. 

The  facts  are  that  climate  everywhere  does  fluctuate  quite  noticeably 
from  year  to  year  and  that  there  are  gradual  changes  in  climate  that 
make  one  decade  or  one  century  different  from  the  one  before.  These 
yearly  fluctuations  and  longer  term  changes  have  been  the  result  of 
natural  processes  or  external  influences  at  work  on  the  complex  system 
that  determines  Earth's  climate.  It  is  a  system  that  seems  to  strive  for 
a  balance  among  atmosphere,  oceans,  land,  and  polar  ice  masses — all 

9  Barrett,  Earl  W.,  "Inadvertent  Weather  and  Climate  Modification."  Crtiical  Reviews  in 
Environmental  Control,  vol.  6,  No.  1,  December  1975,  pp.  15-90. 


influenced  by  possible  solar  and  cosmic  variations  of  which  climate 
researchers'  knowledge  is  in  some  cases  nonexistent,  or  incomplete,  and 
otherwise  tenuous  at  best.  Society  itself  is  becoming  another  significant 
factor  in  the  climatic  balance. 

It  is  no  news,  for  example,  that  the  atmosphere  of  large  midlatitude 
cities  is  both  warmer  and  more  turbid  than  the  surrounding  country- 
side (particularly  in  winter)  as  a  result  of  thermal  and  chemical  pol- 
lution and  to  some  extent  because  of  the  ability  of  groups  of  buildings 
to  trap  heat  from  the  Sun.  There  is  also  good  evidence  for  increased 
summertime  rainfall  downwind  from  cities  such  as  St.  Louis,  Chicago, 
and  Paris.10  Indeed,  it  is  very  likely  that  the  industrialization  of  siz- 
able regions,  such  as  the  eastern  United  States  and  western  Europe, 
has  modified  their  climates  in  certain  more  subtle  ways.  In  any  attempt 
to  assess  a  manmade  climatic  effect,  it  is  essential  to  understand  and 
have  a  measure  of  the  degree  of  climatic  variability  which  may  be 
expected  in  the  absence  of  human  influence. 

The  concept  of  climatic  change  and  variability 

The  concept  of  climatic  change  and  variability  entails  a  wide  range 
of  complex  interactions  with  a  disparity  of  response  times  among  the 
air,  sea,  ice,  land,  and  biotic  components  of  the  climate  system.  Climate 
is  not  a  fixed  element  of  the  natural  environment.  Indeed,  important 
advances  in  climate  research  and  the  study  of  former  climates  confirm 
that  past  climates  of  Earth  have  changed  on  virtually  all  resolvable 
time  scales.  This  characteristic  suggests  that  there  is  no  reason  to 
assume  the  favorable  climatic  regime  of  the  last  several  decades  is 
permanent  and,  moreover,  that  climatic  change  and  variability  must 
be  recognized  and  dealt  with  as  a  fundamental  property  of  climate. 

In  this  matter  it  is  important  to  appreciate  the  fact  that  a  renewed 
appreciation  of  the  inherent  variability  of  climate  has  manifested 
itself  in  the  public  consciousness.  Climate  has  not  become  suddenly 
more  variable  in  a  way  that  it  has  never  been  variable  before,  but  events 
of  recent  years 11  have  shaken  a  somewhat  false  sense  of  technological 
invulnerability.  Thus,  climatic  variability  is  a  media  item  now  because 
society  ignored  for  so  long  its  continued  dependence  on  the  ecological/ 
climatic  balance  achieved,  and  then  failed  to  plan  systematically  for 
the  coming  unfavorable  years,  which  eventually  had  to  come — and 
always  will,  given  the  nature  of  the  atmosphere.  It  is  more  palatable 
to  blame  climate  for  present  predicaments  than  to  acquiesce  to  a  lack 
of  preparedness.  As  F.  Kenneth  Hare,  climatologist  with  the  Science 
Council  of  Canada,  has  noted : 

It  is  paramount  that  the  [climate- related]  events  of  1972  do  not  repeat  them- 
selves, even  if  bad  weather  does.  It  does  not  matter  whether  such  events  are  part 
of  a  genuine  change  in  climate  or  are  merely  unusually  large  fluctuations  of  a 
basically  unchanging  system.  In  fact,  I  doubt  whether  such  arguments  mean  any- 
thing. It  does  matter  that  climatic  extremes  do  occur ;  that  they  have  recently 
become  rather  frequent  and  have  had  severe  impacts ;  that  we  lack  the  predic- 

10  Dettwiller,  J.  W.  and  S.  A.  Changnon,  "Possible  Urban  Effects  on  Maximum  Daily 
Rainfall  Rates  at  Paris,  St.  Louis,  and  Chicago."  Journal  of  Applied  Meteorology,  vol.  15, 

May  1976.  pp.  517-519. 

11  Most  of  the  world's  important  grain-growing  regions  experienced  unfavorable  weather 
and  crop  failures  in  1972  or  1974.  or  both.  Tbo  winter  of  1977  was  perceived  by  most  Amer- 
icans as  remarkably  abnormal,  with  severe  cold  in  the  East  (coldest,  in  fact,  since  the 
founding  of  the  Republic),  drought  in  the  West,  and  mild  temperatures  ns  far  north  as 
Alaska  :  and  the  summer  of  1977  was  one  of  the  two  or  three  hottest  in  the  last  100  years 
over  most  of  the  United  States. 


tive  skill  to  avoid  impacts  on  food  production — and  energy  consumption;  and 
that  we  [the  atmospheric  science  community]  are  insufficiently  organized  to  make 
maximum  use  of  existing  skill.12 

While  scientists  concur  that  climate  is  not  a  fixed  component  of  the 
natural  environment,  there  is  less  agreement  with  regard  to  when 
and  how  climatic  change  occurs.  Although  in  the  long  term  a  major 
natural  change  to  a  different  climatic  regime  may  be  expected,  it  is 
unlikely  that  any  trend  toward  such  a  change  would  be  perceptible  in 
the  near  term,  as  it  could  be  obscured  by  large  amplitude,  shorter  term 
climatic  variability.  Considered  from  a  historical  perspective,  and 
judging  from  the  record  of  past  interglacial  ages,  climatic  data  indi- 
cate that  the  long-term  trend  over  the  next  20,000  or  so  years  is  toward 
a  cooling  cycle,  a  cooler  climate,  and  eventually  the  next  glacial  age. 
The  onset  of  that  change  may  be  a  number  of  centuries  or  millennia 
away ;  conceivably  it  may  already  have  begun.  In  recent  years,  books 
and  newspaper  stories  have  conditioned  us  to  expect  colder  weather  in 
the  future.  In  geological  perspective,  the  case  for  cooling  is  strong. 
The  modern-day  world  is  experiencing  an  interglacial  period,  a  rela- 
tively warm  interlude — lasting  many  thousands  of  years — between 
longer  intervals  of  cold.  If  this  interglacial  age  lasts  no  longer  than  a 
dozen  earlier  ones  in  the  past  million  years,  as  recorded  in  deep-sea 
sediments,  we  may  reasonably  suppose  that  the  world  is  about  due  to 
begin  a  slide  into  the  next  ice  age.  It  does  seem  probable,  though,  that 
this  transition  would  be  sufficiently  gradual  so  that  in  the  next  100  to 
200  years  it  would  be  almost  imperceptible  amid  the  ubiquitous  varia- 
bility of  climate.13, 14> 15 

Considering  the  much  more  recent  past,  climatologists  point  out 
that  the  world  has  been  in  the  throes  of  a  general  cooling  trend  during 
the  last  SO  or  40.  years.  Because  this  modern-day  cooling  trend  has 
sometimes  been  misinterpreted  as  an  early  sign  of  the  approach  of  an 
ice  age  (it  really  is  only  one  of  many  irregular  ups  and  downs  of 
climate  that  mankind  has  witnessed  through  Jiistory ) ,  it  has  reenf  orced 
the  popular  notion  that  our  future  is  likely  to  be  a  cold  one.  (In  point 
of  fact,  this  cooling  trend  has  been  faltering  in  very  recent  years,  and 
may  already  have  started  to  reverse  itself.) 

Writes  research  climatologist  J.  Murray  Mitchell,  Jr. : 

I  agree  with  those  climatologists  who  say  that  another  ice  age  is  inevitable. 
I  strongly  disagree,  however,  with  those  who  suggest  that  the  arrival  of  the  next 
ice  age  is  imminent,  and  who  speak  of  this  as  the  proper  concern  of  modern 
civilization  in  planning  for  the  next  few  decades  or  centuries.  Should  nature  be 
left  to  her  own  devices,  without  interference  from  man,  I  feel  confident  in  pre- 
dicting that  future  climate  would  alternately  warm  and  cool  many  times  before 
shifting  with  any  real  authority  toward  the  next  ice  age.  It  would  be  these 
alternate  warmings  and  coolings,  together  with  more  of  the  same  ubiquitous, 
year-to-year  variability  of  climate  that  has  always  been  with  us,  that  would  be 
the  appropriate  object  of  our  concerns  about  climate  in  the  foreseeable  future.16 

12Norwine,  Jim,  "A  Question  of  Climate,"  Environment,  vol.  19,  No.  8,  November  1977, 
p.  12. 

13  National  Research  Council,  U.S.  Committee  for  the  Global  Atmospheric  Research  Pro- 
gram, Understanding  Climntic  Change :  A  Program  for  Action,  Washington,  National 
Academy  of.Sciences.  1975,  239  pp. 

14  U.S.  Federal  Council  for  Science  and  Technology  Interdepartmental  Committee  for 
Atmospheric  Sciences,  report  of  the  Ad  Hoc  Panel  on  the  Present  Interglacial,  Washington, 
National  Science  Foundation.  1974.  22  pp.  (ICAS  lSb-FY75). 

15  United  Nations.  World  Meteorological  Organizations  (WMO).  WMO  Statement  on  Cli- 
matic Chance,  pt.  B  :  technical  report,  p  9. 

19  Mitchell  J.  Murray.  Jr..  "Carbon  Dioxide  and  Future  Climate,"  EDS  [Environmental 
Data  Service]  magazine,  March  1977,  p.  4. 


Because  of  man's  presence  on  the  Earth,  however,  what  will  actually 
happen  in  future  decades  and  centuries  may  well  follow  a  different 
scenario ;  imperceptibly  different  at  first,  but  significantly  so  later  on, 
covering  a  full  spectrum  of  climatic  possibilities  ranging  from  warm- 
ing to  cooling  trends.  Varying  interpretations  of  this  evidence  have 
led,  on  one  hand,  to  a  scientifically  valid  caution  regarding  possible 
instability  of  present-day  climate  conditions  and,  on  the  other  hand,  to 
predictions  that  the  Earth  may  be  on  the  verge  of  a  new  climate  regime, 
which  implies  a  new  equilibrium  among  the  elements  of  the  climatic 
system,  involving  a  somewhat  different  set  of  constraints  and,  almost 
certainly,  noticeable  regional  shifts  of  climate.  Climate  researchers 
iteratively  emphasize  the  importance  of  recognizing  and  appreciating 
the  inherent  variability  of  climate,  a  fact  which  may  be  more  signifi- 
cant than  the  uncertainty  of  whether  recent  events  portend  a  trend 
toward  a  warmer  or  cooler  climate  of  the  future. 

When  and  how  do  climatic  changes  occur? 

So  far,  there  is  no  single  comprehensive  theory,  or  even  a  combina- 
tion of  a  small  number  of  theories,  that  completely  explains — much  less 
predicts — climatic  fluctuations  or  change.  As  yet,  there  is  no  deter- 
ministic, predictive  model  of  our  planet's  climate,  and,  until  one  is 
developed,  predictions  are  as  valid  as  the  logic  producing  them.  The 
periods  of  time  involved  in  climatic  predictions  cover  centuries,  and 
the  validity  of  climate  forecasting  is  not  easily  tested.  Nevertheless, 
there  are  some  factors  and  processes  that  clearly  should  be  taken  into 
account,  either  in  terms  of  observed  correlations  in  the  past  or  of 
theoretical  assumptions  about  what  should  be  important.  All,  in  one 
way  or  another,  effect  changes  and  variability  of  climate  by  modifying 
the  natural  thermal  balance  of  the  atmosphere. 

One  group  of  processes  responsible  for  climatic  change  and  varia- 
bility consists  of  external  mechanisms,  including:  fluctuations  of  the 
Sun's  radiative  output,  variations  of  Earth's  orbital  parameters, 
changes  in  atmospheric  dust  content,  changes  in  levels  of  carbon  diox- 
ide and  ozone  in  the  atmosphere,  and  migration  of  land  masses  and 
shifting  of  continental  plates. 

In  addition  to  being  influenced  by  external  forcing  mechanisms, 
climate  is,  to  a  certain  degree,  regulated  by  processes  internal  to  the 
climatic  system,  involving  "feedback"  interactions  between  the  at- 
mosphere, the  world  ocean,  the  ice  masses,  the  land  surface,  and  the 
biosphere.  If  an  external  variable  were  to  be  changed  by  a  certain  fac- 
tor, the  response  of  the  climatic  system  to  that  change  could  be  modi- 
fied by  the  actions  of  these  internal  processes  which  act  as  feedbacks 
on  the  climatic  system  modifying  its  evolution.  There  are  some  feed- 
backs which  are  stabilizing,  and  some  which  are  destabilizing;  that  is, 
they  may  intensify  deviations. 

In  all  likelihood,  climatic  change  is  a  function  of  various  combina- 
tions of  interacting  physical  factors,  external  processes,  internal  proc- 
esses, and  synergistic  associations  (see  fig.  2),  but  it  is  not  yet  clear  to 
what  extent  the  observed  variability  of  the  climatic  system  originates 
from  internal  mechanisms,  and  to  what  extent  from  external  mecha- 
nisms. It  appears  likely  that  the  answer  depends  upon  the  time  scale 
of  variability,  with  internal  processes  probably  important  on  the  scale 
of  months  and  decades,  and  external  mechanisms  becoming  increas- 
ingly important  on  time  scale's  beyond  a  cent  ury  as  depicted  in  figure  3. 


Changes  of 
Solar  Radiation 




H,0,  NJ(  Oj,  COJ(  03,  etc. 


atmosphere-land  coupling     atmosphere-ice  coupling 

changes  of 
atmospheric  composition 

changes  of  land  features, 
orography,  vegetation, 
albedo,  etc. 

Figure  2. — Schematic  illustration  of  the  components  of  the  coupled  atmosphere- 
ocean-ice-land  surface-biota  climatic  system.  The  full  arrows  are  ex- 
amples of  external  mechanisms,  and  the  open  arrows  are  examples  of 
internal  mechanisms  of  climatic  change. 

Source:  Living  With  Climatic  Change.  Proceedings  of  a  conference/workshop  held  in 
Toronto,  November  17-22,  1975.  Ottawa,  Science  Council  of  Canada,  1976,  p.  85. 

SoUr  Variability 

Earth's  Rotation, 
Polar  Wandering 


Continental  Drift 

Sea-Floor  Spreading 
-* —  Mountain  Building 

Atmospheric  Mass,  Composition,  Volcanic  Dust 

♦   Orbital   »- 


"  Glaciers 

Continental  Ice  Sheets 

Sea  Ice 


Sea-level,  Lake  Level,  Isostatic  Adjustment 

Oceanic  Composition, 




-*  Bottom  — 



GLACIAL        —  Vegetal  Cover 


Ocean  Layer 

Man's  Land  Use 

-Pollutants,  CO, 

Autovariation  of 

of  Atmosphere 

I  I 





10*         10*  10* 
Time  in  years 



Figure  3.— Characteristic  climatic  events  and  processes  in  the  atmosphere,  hydro- 
sphere, cryosphere.  lithosphere,  and  biosphere  and  possible  causative  factors  or 
global  climatic  change. 

Source  :  National  Research  Council.  U.S.  Committee  for  the  Global  Atmospheric  Research 
Program.  Understanding  Climatic  Change  :  A  Program  for  Action.  Washington,  National 
Academy  of  Sciences,  1975,  p.  22. 


For  a  comprehensive  and  detailed  discussion  of  the  mechanisms  and 
factors  governing  climatic  change  and  variability,  see  "A  Primer  on 
Climatic  Variation  and  Change"  ( 1976)  .17 

The  possibility  also  exists  that  society  may  be  changing  the  climate 
through  its  own  actions  by  pushing  on  certain  leverage  points.  Our 
presence  on  Earth  cannot  be  assumed  to  go  unnoticed  by  the  atmos- 
phere, and  human  intervention  now  presents  possibilities  that  have 
never  existed  in  the  historic  or  geologic  past.  At  question  is  whether 
the  effects  of  civilized  existence  are  yet  capable  of  altering  Earth's 
heat  balance  and,  hence,  impacting  climate  on  a  global  scale  to  an  im- 
portant extent.  Enormous  amounts  of  gaseous  and  particulate  mate- 
rials have  been  emitted  into  the  atmosphere  through  the  combustion 
of  fossil  fuels  (primarily  carbon  dioxide,  sulfur  dioxide,  and  fly  ash) 
and  through  the  manipulation  of  land  for  agriculture  and  commerce 
(primarily  windblown  dust,  and  forest  and  grass  fire  smoke).  To 
an  increasing  extent,  waste  heat  is  also  entering  the  atmosphere,  both 
directly  and  indirectly  (via  rivers  and  estuaries)  and  in  both  sensible 
and  latent  form  (as,  for  example,  through  evaporation  in  wet  cooling 
towers).  Moreover,  large-scale  land  management  programs  have  been 
responsible  for  significant  changes  in  reflective  properties,  moisture 
holding  capacity,  and  aerodynamic  roughness  of  the  surface  (pri- 
marily through  deforestation,  water  impoundment  by  manmade  lakes, 
slash-burn  agriculture  practices,  urbanization,  and  so  forth).  In  view 
of  the  growth  of  population,  industry,  food  production,  and  commerce 
in  the  years  and  decades  ahead,  the  time  is  almost  certainly  not  far 
off  when  human  effects  on  large-scale  climate  would  become  appreci- 
able in  relation  to  natural  phenomena  leading  to  changes  and  vari- 
ability of  climate. 

It  does  seem  likely  that  industrial  man  already  has  started  to  have 
an  impact  on  global  climate,  although  this  is  difficult  to  prove  by  direct 
observation,  because  the  impact  is  not  easily  recognizable  amid  the 
large  natural  variability  of  climate.  "If  man  continues  his  ever- 
growing consumption  of  energy,"  contends  J.  Murray  Mitchell,  "and 
in  the  process  adds  further  pollution  to  the  global  atmosphere,  it  may 
not  be  very  many  years  or  decades  before  his  impact  will  break  through 
the  'noise  level'  in  the  record  of  natural  climatic  variability  and 
become  clearly  recognizable." 18  Furthermore,  the  most  significant 
impacts  that  mankind  would  probably  have  on  the  climatic  system 
are  apparently  all  in  the  same  direction  as  far  as  global  mean  tempera- 
tures are  concerned  and  are  likely  to  constitute  a  warming  trend.19 

The  Facts  About  Inadvertent  Weather  and  Climate  Modification 
airborne  particulate  matter  and  atmospheric  turbidity 

Particulate  matter  in  the  atmosphere  may  significantly  affect  climate 
by  influencing  the  Earth's  radiation  balance  (figure  4)  and/or  cloud 
nucleation  and  precipitation. 

17  Justus.  John  R..  "Mechanisms  and  Factors  Governing  Climatic  Variation  and  Change.'' 
In  "A  Primer  on  Climntic  Variation  and  Change,"  prepared  by  the  Congressional  Research 
Service,  Library  of  Congress,  for  the  Subcommittee  on  the  Environment  and  the  Atmosphere 
of  the  Committee  on  Science  and  Technology.  U.S.  House  of  Representatives.  94th  Cong., 
2d  sess.  (committee  print).  Washington.  U.S.  Government  Printing  Office,  197G,  pp.  77-127. 

18  Mitchell,  J.  Murrav.  Jr..  "Carbon  Dioxide  and  Future  Climate,"  p.  4. 

Jt>  Kellogg.  William  W..  "Is  Mankind  Warming  the  Earth?"  Bulletin  of  the  Atomic  Scien- 
tists, vol.  34,  February  1978,  pp.  10-19. 


Do  more  particles  mean  a  warming  or  cooling? 

There  is  a  question  as  to  whether  more  particles  mean  a  warming 
or  cooling  of  the  lower  atmosphere.  The  general  cooling  trend  of  the 
last  30  to  40  years  (which  some  experts  feel  may  have  bottomed  out 
and  already  started  to  reverse  itself)  could  have  been  a  result  of  a 
reduction  of  solar  radiation  reaching  the  surface  of  the  Earth  because 
of  particulates  that  have  been  scattered  into  the  atmosphere  by  man's 
activities,  among  them :  the  burning  of  fossil  fuels,  mechanized  agri- 
cultural operations,  overgrazing  of  arid  lands,  manmade  forest  fires, 
and  the  slash -burn  method  of  clearing  land  for  crops,  which  is  still 
widely  employed  in  the  Tropics.  But  if  man  started  his  polluting 
processes  in  the  last  century,  and  the  decrease  of  global  temperature 
were  due  to  alteration  in  the  transparency  of  the  atmosphere,  then 
why  has  a  decrease  in  temperature  not  been  observed  earlier?  It  is 
possible  that  instruments  were  measuring  a  natural  climatic  trend 
that  may  have  been  only  somewhat  augmented  by  the  byproducts  of 
resource  development,  power  generation,  and  industrial  activities. 

The  situation  is  such  that  the  net  effect  of  a  given  particle  on  Earth's 
heat  balance  and  hence  on  climate  depends,  in  large  part,  upon  the 
nature  (number  and  size)  of  the  particles,  where  in  the  atmosphere 
they  are  found,  and  how  long  they  remain  suspended.  Some  aerosols, 
such  as  lead  from  auto  exhaust,  are  rapidly  scavenged  by  precipitation. 
Others,  mostly  organic  particles  such  as  pesticides,  may  remain  for 
months  or  years.  While  short-term  aerosols  such  as  lead  may  affect 
weather  on  a  local  scale,  it  is  the  aerosols  that  remain  and  accumulate 
in  the  atmosphere  that  will  have  long-term  effects  on  climate. 

Figure  4. — The  mean  annual  radiation  and  heat  balance  of  the  atmosphere, 
relative  to  100  units  of  incoming  solar  radiation,  based  on  satellite  measure- 
ments and  conventional  observations. 

Source  :  National  Research  Council.  U.S.  Committee  for  the  Global  Atmospheric  Research 
Program.  Understanding  Climatic  Change  :  A  Program  for  Action,  Washington,  National 
Academy  of  Sciences,  1975,  p.  18. 

34-857  O  -  79  -  13 


Idso  and  Brazel  reporting  on  their  research  results  in  the  November 
18,  1977  issue  of  Science  magazine  found  that  initial  increases  in 
atmospheric  dust  concentration  tend  to  warm  the  Earth's  surface. 
After  a  certain  critical  concentration  has  been  reached,  continued  dust 
buildup  reduced  this  warming  effect  until,  at  a  second  critical  dust 
concentration,  a  cooling  trend  begins.  But,  they  explain,  this  second 
critical  dust  concentration  is  so  great  that  any  particulate  pollution  of 
the  lower  atmosphere  will  have  the  inexorable  tendency  to  increase 
surface  temperatures.  The  authors  pointed  out  that  if,  and  when,  man- 
generated,  industrial  pollution  of  the  atmosphere  as  a  source  of  par- 
ticulates ever  becomes  climatologically  significant,  the  resultant  sur- 
face temperature  trend  will  definitely  be  one  of  warming,  not  cooling. 
Thus,  whereas  many  groups  assigned  to  assess  the  problem  have  looked 
on  this  aspect  of  intensified  industrialization  as  acting  as  a  "brake" 
on  the  warming  influence  inferred  lately  of  increased  carbon  dioxide 
production,20  just  the  opposite  is  actually  the  case — the  two  phenomena 
could  tend  to  complement  each  other.21 

Sources  of  atmospheric  particulates:  natural  against  manmade 

Of  course,  not  all  aerosols  in  the  Earth's  atmosphere,  or  even  a  major 
proportion,  are  attributable  to  human  activity.  In  fact,  dust  from  vol- 
canic eruptions,  sea  salt  from  evaporated  ocean  spray,  smoke  from 
lightning-caused  forest  fires  (see  fig.  5),  debris  from  meteors  which 
burn  up  in  the  atmosphere,  windblown  dust  or  sandstorms,  and  organic 
compounds  emitted  by  vegetation  are  much  larger  sources  of  atmos- 
pheric particulates  than  human  activity.  Scientists  at  Stanford  Uni- 
versity estimate  that  natural  processes  produce  about  2,312  million 
tons  of  aerosols  a  year,  which  amount  to  88.5  percent  of  the  total. 
Man  and  his  activities  account  for  only  296  million  tons,  the  remaining 
11.5  percent.  At  present,  it  is  unlikely  that  man's  activities  and  man- 
made  aerosols  will  affect  global  temperatures.  It  is  important  to  note, 
however,  that  while  aerosols  from  natural  sources  are  distributed 
fairly  evenly  across  the  planet,  man,  in  contrast,  contributes  high  con- 
centrations mostly  from  industrial  centers.  Atmospheric  scientists  at 
the  National  Oceanic  and  Atmospheric  Administration's  Atmospheric 
Physics  and  Chemistry  Laboratory  found  that  the  296  million  tons  of 
manmade  aerosols  are  produced  every  year  on  only  about  2.5  percent 
of  the  surface  of  the  globe.  Within  these  limited  areas,  manmade 
aerosols  account  for  nearly  84  percent  of  the  total.  It  follows,  then, 
that  these  aerosols  may  be  expected  to  have  noticeable  effects  on  local 
weather  and  urban  climates. 

20  See,  generally,  National  Research  Council.  Geophysics  Research  Board,  "Energy  and 
Climate,"  Washington,  National  Academy  of  Sciences,  1977,  281  pp. 

21  Idso,  Sherwood  B.  and  Anthony  J.  Brazel,  "Planetary  Radiation  Balance  RB  a  Function 
of  Atmospheric  Dust :  Climatological  Consequences,"  Science,  vol.  198,  Nov.  18,  1977,  pp. 


Figure  5. — Not  all  aerosols  in  the  Earth's  atmosphere  are  attributable  to  human 
activity.  In  this  Landsat  photo,  smoke  from  a  fire  in  the  Seney  National  Forest, 
upper  peninsula  of  Michigan,  serves  as  a  source  of  atmospheric  particulates. 
Note  the  extent  of  the  dust  veil  downwind  of  the  source.  ( Courtesy  of  National 
Aeronautics  and  Space  Administration. ) 

Atmospheric  processes  affected  by  particles 

Everyday,  particles  of  soot,  smoke,  dust,  and  chemicals  from  indus- 
trial combustion  and  other  activities  are  emitted  into  the  urban  atmos- 
phere. About  80  percent  of  the  solid  contaminants  are  small  enough  to 
remain  suspended  in  the  air,  sometimes  for  several  days.22  Even  though 
these  tiny  particles  reflect  and  scatter  sunlight  ostensibly  keeping  its 
heat  from  reaching  the  ground,  they  also  can  act  as  a  lid  to  prevent 
the  outflow  of  heat  from  the  land  surface  to  the  atmosphere.  In  a  sense, 
this  turbidity  acts  as  an  insulator.  It  reduces  the  amount  of  sunlight 
received  at  the  top  of  the  city  in  the  daytime  and  cuts  down  on  a  source 
of  heat.  However,  at  night  urban  aerosol  pollutants  retard  the  depar- 
ture of  radiant  energy  from  the  heated  city  air,  encasing  the  heat  in 

22  "Do  Cities  Change  the  Weather?"  Mosaic,  vol.  5,  summer  1974,  pp.  33,  34. 


the  city's  closed  atmospheric  system.  Certain  aerosols  may  undergo 
chemical  change  when  they  combine  with  water  vapor  in  the  presence 
of  solar  radiation.  There  are  many  complicated  processes  that  can 
generate  aerosol  gas-to-particle  conversions,  and  the  particles  can  then 
grow  by  surface  chemistry  and  physical  accretion.23 

Perhaps  the  most  sensitive  atmospheric  processes  which  can  be 
affected  by  air  pollutants  are  those  involved  in  the  development  of 
clouds  and  precipitation.  The  formation  and  building  of  clouds  over 
a  city  can  be  influenced  by  the  presence  of  pollutants  acting  as  nuclei 
upon  which  water  vapor  condenses  and  by  the  hot  dry  air  with  which 
these  aerosols  are  swept  into  the  base  of  the  clouds  (see  fig.  6).  The 
structure  of  clouds  with  temperatures  below  0°  C  (defined  as  cold 
clouds)  can  be  modified,  and  under  certain  conditions  precipitation 
from  them  altered,  by  particles  which  are  termed  ice  nuclei.24  The  con- 
centrations of  natural  ice  nuclei  in  the  air  appear  to  be  very  low :  Only 
about  one  in  a  billion  atmospheric  particles  which  are  effective  as  ice 
nuclei  at  temperatures  above  about  — 15°  C  have  the  potential  for  mod- 
ifying the  structure  of  clouds  and  the  development  of  precipitation. 
If  the  concentration  of  anthropogenic  ice  nuclei  is  about  1  in  100  mil- 
lion airborne  particles,  the  result  may  be  an  enhancement  of  precipita- 
tion ;  however,  if  the  concentration  is  greatly  in  excess  of  1  in  100  mil- 
lion, the  result  may  be  a  tendency  to  "overseed"  cold  clouds  and  reduce 
precipitation.  Certain  steel  mills  have  been  identified  as  sources  of  ice 
nuclei.  Also  of  concern  is  the  possibility  that  emissions  from  automo- 
biles may  combine  with  trace  chemicals  in  the  atmosphere  to  produce 
ice  nuclei.25 

23  Hobhs.  P.  V..  H.  Harrison,  E.  Robinson,  "Atmospheric  Effects  of  Pollutants."  Science, 
vol.  183,  Mar.  8,  1974.  p.  910. 

2i  National  Research  Council.  Committee  on  Atmospheric  Sciences.  "Weather  and  Climate 
Modification  :  Problems  and  Progress,"  Washington,  National  Academy  of  Sciences,  1973, 
pp.  41-47. 

25  Hobbs,  P.  V.,  H.  Harrison,  E.  Robinson,  "Atmospheric  Effects  of  Pollutants,"  p.  910. 


Figure  6. — The  formation  and  building  of  clouds  can  be  influenced  by  the  pres- 
ence of  pollutants  acting  as  nuclei  upon  which  water  vapor  condenses  and  by  the 
hot  dry  air  with  which  these  aerosols  are  swept  aloft.  In  this  Landsat  photo, 
excess  particles  as  well  as  heat  and  moisture  produced  by  the  industries  of  Gary, 
Ind..  favor  the  development  of  clouds  downwind.  The  body  of  water  shown  is 
the  southern  tip  of  Lake  Michigan.  (Courtesy  of  National  Aeronautics  and 
Space  Administration.) 

Precipitation  from  clouds  that  have  temperatures  above  0°  C  (warm 
clouds)  may  be  modified  by  particles  which  serve  as  cloud  condensa- 
tion nuclei  (CCN).  A  source  that  produces  comparatively  low  con- 
centrations of  very  efficient  CCN  will  tend  to  increase  precipitation 
from  warm  clouds,  whereas  one  that  produces  large  concentrations 
of  somewhat  less  efficient  CCN  might  decrease  precipitation.  Modi- 
fications in  the  structure  of  clouds  and  precipitation  have  been  observed 


many  miles  downwind  of  fires  and  pulp  and  paper  mills.  Large  wood- 
waste  burners  and  aluminum  smelters  have  also  been  identified  as 
major  sources  of  CCN.26 

The  La  Porte  tveather  anomaly:  urban  climate  modification 

La  Porte,  Ind.,  is  located  east  of  major  steelmills  and  other  indus- 
tries south  of  Chicago.  Analysis  of  La  Porte  records  revealed  that, 
since  1925,  La  Porte  had  shown  a  precipitation  increase  of  between 
30  and  40  percent.  Between  1951  and  1965,  La  Porte  had  31  percent 
more  precipitation,  38  percent  more  thunderstorms,  and  246  percent 
more  hail  days  than  nearby  weather  stations  in  Illinois,  Indiana, 
and  Michigan.27  Reporting  on  this  anomaly  at  a  national  meeting  of 
the  American  Meteorological  Society  in  1968,  Stanley  Changnon,  a 
climatologist  with  the  Illinois  State  Water  Survey  pointed  out  that 
the  precipitation  increase  in  La  Porte  closely  followed  the  upward 
curve  of  iron  and  steel  production  at  Chicago  and  Gary,  Ind.  Fur- 
thermore, La  Porte's  runs  of  bad  weather  correlated  closely  with 
periods  when  Chicago's  air  pollution  was  bad.  Stated  simply,  Ohang- 
non's  theory  was  that  if  this  effect  did  not  occur  by  chance,  then  the 
increase  in  precipitation  comd  be  caused  by  the  excess  particles 
as  well  as  heat  and  moisture  produced  by  the  industries  upwind 
of  La  Porte.  Pollutants  from  the  industrial  sources,  it  seemed,  were 
serving  as  nuclei  to  trigger  precipitation,  just  as  silver  iodide  crystals 
are  used  to  seed  clouds  in  deliberate  efforts  of  weather  modification.28 
The  discovery  of  the  La  Porte  anomaly  helped  usher  in  considerable 
scientific  and  public  concern  as  to  whether  cities  could  measurably 
alter  precipitation  and  severe  weather  in  and  downwind  of  them.  A 
large  urban-industrial  center  is  a  potential  source  of  many  conditions 
needed  to  produce  rainfall.  These  include  its  release  of  additional 
heat  (through  combustion  and  from  "storage"  in  surfaces  and  build- 
ings) which  lifts  the  air ;  the  mechanical  mixing  due  to  the  "mountain 
effects"  of  a  city  existing  in  flat  terrain ;  additional  moisture  released 
through  cooling  towers  and  other  industrial  processes ;  and  the  addi- 
tion  of  many  small  particles  (aerosols),  which  could  serve  as  nuclei 
for  the  formation  of  cloud  droplets  and  raindrops. 

The  interest  in  whether  urban  emissions  into  the  atmosphere  could 
trigger  changes  in  weather  and  climate  on  a  scale  much  larger  than 
the  city  itself  led  to  climatological  studies  of  other  cities.  Historical 
data  for  1901-70  from  Chicago.  St.  Louis,  Washington,  D.C.,  Cleve- 
land, Xew  Orleans,  Houston,  Indianapolis,  and  Tulsa  were  studied  in 
an  effort  to  discern  whether  cities  of  other  sizes,  different  industrial 
bases,  and  varying  climatic-physiographic  areas  also  experienced  rain- 
fall changes.  The  six  largest  cities — Washington,  Houston,  New 
Orleans,  Chicago,  Cleveland,  and  St.  Louis — all  altered  their  summer 
precipitation  in  a  rather  marked  fashion:  Precipitation  increases  of 
LOto  30  percenl  in  and  downwind  of  t  heir  urban  locales,  plus  associated 
increases  in  thunderstorm  and  hailstorm  activity  were  documented. 

16  National  Research  Council.  Committee  on  Atmospheric  Sciences,  "Weather  and  Climate 
Modification  :  Prohlems  and  Progress."  p.  50. 

»  Lansford.  Henry,  "We're  Changing  the  Weather  hy  Accident,"  Science  Digest,  vol.  74, 
Dec.  1973,  p.  21. 

M  Changnon.  S.  A.,  Jr..  "The  La  Porte  Weather  Anomaly — Fact  or  Fiction?"  Bulletin  of 
the  American  Meterologlcal  Society,  vol.  49,  January  19G8,  pp.  4-11. 


Tulsa  and  Indianapolis,  cities  of  lower  population  and  lesser  physio- 
graphic irregularities  than  the  others  studied,  did  not  reveal  any 
precipitation  anomalies.29 

The  key  questions  that  could  not  be  answered  conclusively  at  the 
completion  of  these  climatic  studies  were  (1)  whether  the  anomalies 
found  were  real  (or  adequately  measured)  ;  (2)  if  real,  what  was 
causing  the  anomalies;  and  (3)  whether  and  how  extensive  the  anoma- 
lies were  around  other  cities.  To  this  end,  a  major  atmospheric  pro- 
gram dealing  with  inadvertent  weather  modification  was  initiated 
by  a  group  of  scientists  in  1971.  The  Metropolitan  Meteorological 
Experiment  (METROMEX)  was  designed  by  four  research  groups 
who  received  support  from  Federal  agencies  and  one  State  (Illinois). 
St.  Louis  was  chosen  as  the  site  of  extensive  field  investigations  in  this 
first  major  field  program  aimed  at  studying  the  reality  and  causes  of 
urban  rainfall  anomalies  suggested  in  the  climatological  surveys  con- 
ducted previously.30 

Although  data  analysis  and  report  preparation  continue  (summer 
1975  was  the  fifth  and  final  year  for  field  work),  METROMEX  data 
thus  far  portray  statistically  significant  increases  in  summer  rainfall, 
heavy  (more  than  2.5  cm)  rainstorms,  thunderstorms  and  hail  in  and 
just  east  (downtown)  of  St.  Louis.  Examination  of  the  rainfall  yield  of 
individual  showers,  the  spatial  distribution  of  rain  developments,  and 
areal  distribution  of  afternoon  rain  clearly  point  to  the  urban-indus- 
trial complex  as  the  site  for  the  favored  initiation  of  the  rain  process 
under  certain  conditions.31 

Writes  climatologist  Stanley  Changnon : 

The  greater  frequency  of  rain  initiations  over  the  urban  and  industrial  areas 
appears  to  be  tied  to  three  urban-related  factors  including  thermodynamic 
effects  leading  to  more  clouds  and  greater  in-cloud  instability,  mechanical  and 
thermodynamic  effects  that  produce  confluence  zones  where  clouds  initiate,  and 
enhancement  of  the  [raindrop]  coalescence  process  due  to  giant  nuclei.  Case 
studies  reveal  that  once  additional  [rainstorm]  cells  are  produced,  nature,  cou- 
pled with  the  increased  likelihood  for  merger  with  more  storms  per  unit  area, 
takes  over  and  produces  heavier  rainfalls.  Hence  the  city  is  a  focal  point  for 
both  rain  initiation  and  rain  enhancement  under  conditions  when  rain  is  likely.31 

Recapitulating,  METROMEX  researchers  have  found  that  rain, 
thunderstorms  and  hail  can  actually  maximize  within  cities  and  nearby 
areas,  particularly  in  those  downwind.  Such  locations  may  have  more 
storms,  and  they  are  more  intense,  last  longer  and  produce  more  rain 
and  hail  than  storms  in  surrounding  regions.  Apparently,  air  heated 
and  polluted  by  a  city  can  move  up  through  the  atmosphere  high 
enough  to  affect  clouds.  This  urban-modified  air  clearly  adds  to  the 
strength  of  convective  storms  and  increases  the  severity  of  precipita- 
tion. Urban  climatic  alterations  are  summarized  in  table  1. 

29  Huff,  F.  A.  and  S.  A.  Changnon,  Jr.,  "Precipitation  Modification  by  Major  Urban  Areas," 
Bulletin  of  the  American  Meteorological  Society,  vol.  "54,  December  1973,  pp.  1220-1232. 

30  Changnon.  S.  A.,  F.  A.  Huff,  and  R.  G.  Semonin,  "Metromex  :  An  Investigation  of 
Inadvertent  Weather  Modification,"  Bulletin  of  the  American  Meteorological  Society,  vol. 
52,  October  1971,  pp.  958-967. 

si  "METROMEX  Update,"  Bulletin  of  the  American  Meteorological  Society,  vol.  57,  March 
1976,  pp.  304-308. 

32  Changnon,  S.  A.,  R.  G.  Semonin  and  F.  A.  Huff,  "A  Hypothesis  for  Urban  Rainfall 
Anomalies,"  Journal  of  Applied  Meteorology,  vol.  15,  June  1976,  pp.  544-560. 


Table  1. — Some  urban  climatic  alterations  1 

Comparison  with  rural  environs 

Radiation : 

Global    10  to  20  percent  less. 

Ultraviolet : 

Low  sun   30  to  50  percent  less. 

High  sun   5  to  10  percent  less. 

Temperature : 

Annual  mean   1  to  2°  C  higher. 

Maximum  difference   3  to  10°  C  higher. 

Winter  minima   1  to  3°  C  higher. 

Cloudiness : 

General  cloud  cover   5  to  10  percent  more. 


Winter   100  percent  more. 

Summer   20  to  30  percent  more. 

Precipitation : 
Totals : 

Summer   10  percent  more. 

Winter   5  percent  more. 

Relative  humidity  :  Annual  mean   4  to  6  percent  less. 

Evapotranspiration :  Total  amount   30  to  60  percent  less. 

Dew :  Amounts   50  to  80  percent  less. 

Wind  speed  :  <  3  m  sec  -1   40  percent  less. 

Speeds : 

3  —  6  m  sec   20  percent  less. 

>  6  m  sec   10  percent  less. 

Thunderstorms :  Number  of  days   5  to  10  percent  more. 

1  After  Helmut  Landsberg,  University  of  Maryland. 


The  constituent  gases  of  the  atmosphere  that  are  important  vari- 
ables affecting  the  distribution  of  temperature  within  the  atmosphere 
are  carbon  dioxide  and  water  vapor.  Capable  of  absorbing  important 
quantities  of  infrared  radiation,  they  both  have  a  role  in  modifying 
the  vertical  distribution  of  temperature  in  the  atmosphere  by  con- 
trolling the  flux  of  infrared  radiation.  The  absorption  of  incoming 
solar  radiation  by  these  gases  is  so  small  that  their  concentration  has 
no  appreciable  effect  on  the  amount  of  incoming  solar  radiation  reach- 
ing the  Earth's  surface.  Carbon  dioxide  and  water  vapor  are,  how- 
ever, opaque  to  major  portions  of  the  long- wave  radiation  emitted  by 
the  Earth's  surface.  The  greater  the  content  of  these  gases  the  greater 
the  opacity  of  the  atmosphere  to  infrared  radiation  and  the  higher  its 
temperature  must  be  to  radiate  away  the  necessary  amount  of  energy 
to  maintain  a  radiation  balance.  It  is  this  absorption  of  long-wave 
radiation  emitted  by  the  Earth,  with  the  subsequent  reradiation  of 
additional  infrared  radiation  to  the  ground  and  consequent  elevation 
of  air  temperatures  near  the  surface  that  is  known  as  the  "greenhouse 

Increases  in  atmospheric  c<trhon  diowide  concentration:  what  the 
record  indicates 

Man  adds  carbon  dioxide  to  the  atmosphere  through  the  combustion 
of  fossil  fuels,  and  this  addition  is  superimposed  on  the  natural  ex- 
changes between  the  atmosphere,  the  biosphere,  and  the  world  ocean. 
Since  the  use  of  energy  has  increased  exponentially  since  the  beginning 


of  industrialization  around  1860,  it  is  not  surprising  that  the  best 
estimate  of  carbon  dioxide  production,  which  results  from  fossil  fuel 
combustion  and  cement  manufacture,  shows  the  same  exponential 
trend  (see  fig.  7). 

The  concentration  of  carbon  dioxide  in  the  atmosphere  has  in- 
creased steadily  from  a  preindustrial  value  of  about  295  parts  per 
million  in  1860  to  a  current  value  of  330  parts  per  million  (+  12 
percent).  Since  the  beginning  of  accurate  and  regular  measurements 
in  1958,  observed  atmospheric  carbon  dioxide  concentrations  have  in- 
creased some  5  percent  from  315  parts  per  million  to  the  current  yearly 
average  value  of  330  parts  per  million  as  indicated  in  figure  8. 

Figure  7. — The  annual  world  production  of  carbon  dioxide  from  fossil  fuels  (plus 
a  small  amount  from  cement  manufacture)  is  plotted  since  the  beginning  of 
the  industrial  revolution.  Except  for  brief  interruptions  during  the  two  world 
wars  and  the  Great  Depression,  the  release  of  fossil  carbon  has  increased  at  a 
rate  of  4.3  percent  per  year.  (Data  for  1860-1959  from  C.  D.  Keeling,  "Indus- 
trial Production  of  Carbon  Dioxide  from  Fossil  Fuels  and  Limestone,"  Tellus, 
vol.  25,  1973,  p.  174 ;  data  for  1960-71  from  R.  M.  Rotty,  "Commentary  on  and 
Extension  of  Calculative  Procedure  for  Carbon  Dioxide  Production,"  Tellus, 
vol.  25, 1973,  p.  508.) 

Source  :  Baes.  'C.  F..  et  al.  "The  Global  Carbon  Dioxide  Problem,"  Oak  Ridge  National 
Laboratory,  1976.  (ORNL-5194.) 


Figure  8. — Monthly  average  values  of  the  concentration  of  carbon  dioxide  in  the 
atmosphere  at  Mauna  Loa  Observatory,  Hawaii,  are  plotted  since  the  beginning 
of  accurate  and  regular  measurements  in  1958.  Variations  in  photosynthesis  and 
other  seasonal  effects  produce  the  annual  cycle.  Mean  annual  concentrations 
are  well  above  the  preindustrial  level  (290-300  ppm),  and  the  secular  increase 
is  quite  apparent. 

Source:  Baes,  C.  F.,  et  al.  "The  Global  Carbon  Dioxide  Problem,"  Oak  Ridge  National 
Laboratory,  1978.  (ORNL-5194.) 

The  seasonal  variation  of  the  record  of  carbon  dioxide  measurements 
made  at  Mauna  Lao  is  obvious  and  regular,  showing  an  October  mini- 
mum with  increases  in  the  later  autumn  and  winter  months  and  a  maxi- 
mum in  May.  However,  of  greater  importance  to  possible  climatic 
changes  is  the  continued  year-to-year  rise.  Both  the  seasonal  variation 
and  the  annual  increase  have  been  confirmed  by  measurements  at  other 
locations  around  the  globe. 

Predicting  future  atmospheric  carbon  dioxide  levels 

Projecting  the  worldwide  needs  for  energy,  even  with  the  present 
problems,  indicates  a  long-term  global  growth  in  the  consumption  of 
fossil  fuels  and  the  associated  production  of  carbon  dioxide.  Insofar  as 
possible  impact  on  the  climate  is  concerned,  it  is  the  amount  of  carbon 
dioxide  remaining  in  the  atmosphere  that  is  most  important.  In  addi- 
tion to  the  atmosphere,  the  ocean  and  both  land  and  marine  biospheres 
serve  as  reservoirs  for  carbon  dioxide.  Based  on  estimates  of  preindus- 
trial levels  of  atmospheric  carbon  dioxide  of  290-295  parts  per  million 
and  the  1958  to  present  Mauna  Loa  data,  between  58  and  64  percent  of 
the  carbon  dioxide  produced  from  burning  fossil  fuels  remains  in  the 
atmosphere.  Cumulative  production  of  carbon  dioxide  is  plotted  in 
figure  9.  The  upper  set  of  points  indicates  the  increase  in  the  carbon 
dioxide  fraction  of  the  atmosphere  that  would  have  occurred  if  all  car- 


bon  dioxide  produced  since  1860  from  fossil  fuels  and  cement  remained 
airborne.  The  lower  set  of  points  represents  the  observed  increase  based 
on  an  assumed  value  of  290-295  parts  per  million  in  1860.  The  differ- 
ence between  the  two  sets  of  points  presumably  indicates  the  amount  of 
carbon  dioxide  being  taken  up  by  the  world  ocean  and  possibly  the 
biosphere  and  placed  in  long-term  storage.  Nearly  half  of  the  carbon 
dioxide  produced  from  fossil  fuels  and  cement  seems  to  have  found  its 
way  into  reservoirs  other  than  the  atmosphere. 

1  r 

n  r 

i  !  1  1  1     i     i  r 

9  S\c9*- 

I860  1870  1880  1890  1900  1910  1920  1930  1940  1950  1960  1970  1980  1990  2000 


Figure  9. — The  cumulative  production  of  carbon  dioxide  since  1860  is  compared 
with  the  observed  increase  in  the  mean  annual  concentration  since  that  time. 
The  similarity  in  the  rates  of  increase  (about  4  percent  per  year)  produces 
strong  evidence  that  these  two  quantities  are  related.  About  50  percent  of  the 
fossil  carbon  flux  apparently  has  been  balanced,  at  least  since  1958,  by  a 
flow  of  carbon  dioxide  to  such  reservoirs  at  the  world  ocean  and/or  the  land 
biota  (assumed  1860  atmospheric  concentration  equals  295  ppm) . 

Source  :  Baes.  C.  F.,  et  al.  "The  Global  Carbon  Dioxide  Problem,"  Oak  Ridge  National 
Laboratory,  1976.  (ORNL-5194.) 

Future  levels  of  atmospheric  carbon  dioxide  will  depend  primarily 
on  the  rate  of  consumption  of  fossil  fuel  and  to  a  lesser  extent  on  land 
use  patterns  and  practices.  With  brief  interruptions  for  two  world 
wars  and  the  Great  Depression,  the  production  of  carbon  dioxide  from 
fossil  fuels  has  increased  with  an  annual  rate  of  4.3  percent.33  If  the  use 
of  fossil  fuels  continues  to  grow  at  this  present  rate,  the  total  carbon 
dioxide  injected  into  the  atmosphere  by  man  since  1860  wouM  reach 
300  parts  per  million  by  the  year  2030,  and  the  total  concentration 
would  be  equal  to  595  parts  per  million.  This  assumes,  of  course,  no 
change  in  the  average  uptake  by  other  reservoirs  during  this  time. 
Those  energy  scenarios  that  rely  heavily  on  coal,  especially  for  syn- 
thetic oil  and  gas,  yield  estimated  carbon  dioxide  concentrations  of 

33  4.3  percent  per  year  provides  an  excellent  fit  to  the  data  in  figure  7. 


600  parts  per  million  about  the  year  2015  and  1,400  parts  per  miUion 
about  100  years  from  now.  Rotty  and  Weinberg  (1977)  discuss  a 
scenario  by  Niehaus  in  which  nonfossil  energy  sources  dominate  soon 
after  2000.  Even  in  this  case  the  annual  emission  of  carbon  dioxide 
from  fossil  fuel  peaks  at  about  twice  the  present  level  in  the  year  2000 
and  tapers  off  thereafter;  the  atmospheric  concentration  nevertheless 
reaches  475  parts  per  million  by  2050. 34'  35>  36>  37> 38 

Sources  and  sinks  for  carbon  dioxide 

These  extrapolations  are  based  on  certain  assumptions,  a  critical 
one  being  that  the  ocean  and  the  biosphere  will  continue  to  absorb  a 
large  fraction  of  the  carbon  dioxide  in  the  atmosphere.  Some  ocean- 
ographers  see  increasing  evidence  that  the  upper  mixed  layer  of  the 
ocean,  where  most  of  the  carbon  dioxide  is  stored,  is  rapidly  becoming 
saturated,  and  if  this  were  true,  then  it  tends  to  reenforce  the  attain- 
ment of  relatively. high  atmospheric  carbon  dioxide  concentrations  in 
the  next  century.  However,  this  prediction  is  far  from  certain,  because 
carbon  dioxide  absorption  in  the  ocean  could  turn  out  to  be  greater  than 
expected  because  of  mixing  between  ocean  layers  or  other  factors.39 
The  problem  is  further  complicated  by  a  series  of  current  appraisals 
that  suggest  that  the  terrestrial  biomass  appears  to  be  a  net  source  of 
carbon  dioxide  for  the  atmosphere.  George  M.  Woodwell  of  the  Marine 
Biological  Laboratory  at  Woods  Hole,  Mass.,  explains : 

Over  the  past  seven  years  several  reviews  of  the  world  carbon  budget  have  con- 
firmed that  there  is  an  annual  increase  in  the  carbon  dioxide  content  of  [the 
atmosphere]  that  is  worldwide  and  is  almost  certainly  man-caused.  The  source 
of  the  carbon  dioxide  that  is  accumulating  in  the  atmosphere  has  been  commonly 
assumed  to  be  the  combustion  of  fossil  fuels.  Because  the  amount  of  carbon  diox- 
ide accumulating  in  the  atmosphere  is  *  *  *  [about]  half  the  total  released  from 
fossil  fuels,  other  sinks  for  carbon  dioxide  have  been  sought.  The  major  sink  is  the 
ocean,  but  mixing  rates  appear  to  be  too  low  for  the  oceans  to  accommodate  all 
the  carbon  dioxide  that  is  thought  to  be  released  in  excess  of  that  accumulating  in 
the  atmosphere.  The  question  of  whether  the  terrestrial  biota  could  be  another 
sjnk  was  raised  in  1970  [at  SCEP],  and  the  assumption  was  made  that  the  biota 
might  be  a  sink,  especially  in  view  of  the  stimulation  of  photosynthesis  under 
greenhouse  conditions  by  enhanced  concentrations  of  carbon  dioxide.  More  re- 
cently, the  assumption  that  increased  carbon  dioxide  in  air  stimulates  photo- 
synthesis worldwide  has  been  questioned.  So  has  the  assumption  that  the  biota 
is  a  net  global  sink  for  carbon  dioxide.  A  series  of  current  appraisals  suggests 
that,  quite  contrary  to  the  previous  estimates,  the  biota  is  probably  an  addi- 
tional source  of  carbon  dioxide  *  *  *  as  large  as  or  larger  than  the  fossil  fuel 

Thus,  the  great  puzzle  is  the  basic  stability  of  the  global  carbon 
budget.  Without  better  information  on  the  behavior  of  the  terrestrial 
biosphere,  it  is  difficult  to  say  whether  the  biosphere  is  a  sink  or  a 
net  source  of  carbon  dioxide.  If  the  biosphere  is  supplying  more  carbon 

34  Baes,  C.  F..  Jr..  et  al.  "The  Global  Cnrbon  Dioxide  Problem,"  Oak  Ridge,  Tenn.,  Oak 
Ridge  National  Laboratory.  1970.  78  pp.  (ORNL  5194. ) 

*  Lenkowski,  Wil.  "Carbon  Dioxide:  A  Problem  of  Producing  Usable  Data."  Chemical 
and  Engineering  News.  vol.  55,  Oct.  17,  1977  :  pp.  26-30. 

;!0  Rotty,  Ralph  M..  "Energy  and  the  Climate."  Institute  for  Enerprv  Analysis,  Oak  Ridge, 
Oak  Ridge  Associated  Universities.  1970.  28  pp.  ( ORAU/IEA (M)  75-3.) 

37  Rottv.  R.  M.  and  A.  M.  Weinberg.  "How  Long  is  Coal's  Future,"  Climatic  Change,  vol.  1, 
No.  1.  March  1977  :  op.  45-57. 

3*  Rottv.  Ralph  M..  "The  Atmospheric  Carbon  Dioxide  Consequences  of  Heavy  Dependence 
on  Coal."  Institute  for  Energy  Analysis,  Oak  Ridge  Associated  Universities,  occasional 
paper.  32  pp..  Nov.  14,  1977. 

39  Anthes.  Ricbard  A..  Hans  A.  Panofskv.  John  J.  Cnbir  and  Albert  Rango,  "The  Atmos- 
phere." Columbus.  Charles  E.  Merrill  Publishing  Co.,  197r>,  p.  204. 

in  YVoo''"  eii  (i.  M..  ef  al.,  "The  Biota  and  the  World  Carbon  Budget."  Science,  vol.  199, 
Jan.  13,  1978.  pp.  141-146. 


dioxide  than  it  is  absorbing,  then  the  behavior  of  the  ocean  must  be 
different  from  what  oceanographers  believe,  in  the  sense  that  it  would 
be  an  even  more  effective  sink  for  carbon  dioxide  than  previously  sur- 
mised. Thus,  there  is  a  need  for  intense  examination  of  the  flux  of 
carbon  into  the  ocean.  The  ability  of  the  world  ocean  to  act  as  a  carbon 
dioxide  sink  is  large,  but  the  rate  of  possible  sequestering  of  carbon  is 
the  important  factor.  One  possibility  is  that  biotic  mechanisms  in  the 
ocean  are  more  effective  than  has  been  assumed  in  transferring  fixed 
carbon  from  the  mixed  (near-surface)  Jayers  of  the  ocean  into  deep 
ocean  waters.  Before  an  estimate  can  be  made  with  confidence  of  what 
fraction  of  the  carbon  dioxide  from  fossil  fuels  remains  in  the  atmos- 
phere, a  better  understanding  of  the  roles  of  both  the  biosphere  and 
the  world  ocean  in  the  carbon  cycle  is  necessary.41, 42- 43 

Atmospheric  effects  of  increased  carbon  dioxide  levels 

A  change  in  the  carbon  dioxide  content  of  the  atmosphere  upsets 
the  Earth's  radiation  balance  by  holding  back  departing  infrared  light. 
All  things  being  equal,  if  no  other  change  were  to  occur  in  the  system, 
the  net  amount  of  energy  accumulated  by  the  Earth  would  raise  its 
surface  temperature  until  the  enhanced  infrared  emission  reestab- 
lished balance  between  incoming  and  outgoing  radiation.  The  problem, 
however,  is  greatly  complicated  by  the  fact  that  other  changes  would 
certainly  take  place.  For  example,  if  the  Earth's  temperature  rises, 
the  water  vapor  content  of  the  atmosphere  is  likely  to  rise.  More  water 
will  have  the  same  effect  as  more  carbon  dioxide  creating  positive  feed- 
back in  the  system  and  hence  forcing  temperatures  to  climb  even  higher. 
A  rise  in  water  vapor  would  quite  likely  increase  the  fraction  of  the 
globe  covered  by  clouds.  Such  an  increase  would  cause  the  amount  of 
primary  solar  radiation  absorbed  by  the  Earth  to  fall.  Some  combina- 
tion of  increased  temperature  and  cloudiness  will  balance  the  enhanced 
absorption  of  infrared  radiation  by  the  added  carbon  dioxide  and 
water  vapor. 

Implications  of  increasing  atmospheric  carbon  dioxide  concentrations 
The  possibilities  and  implications  of  a  continued  rise  in  the  atmos- 
pheric carbon  dioxide  concentration  were  reviewed  in  a  special  report 
entitled  ''Energy  and  Climate.*'  released  by  the  National  Kesearch 
Council  (NRC)  on  July  25, 1977.44 

The  most  complete,  though  still  imperfect,  climate  models  suggest 
that  a  doubling  of  the  amount  of  carbon  dioxide  in  the  atmosphere, 
relative  to  its  present  amount,  would  increase  the  average  annual 
temperature  of  the  lower  atmosphere  at  middle  latitudes  by  about  2.4° 
to  2.9°  C  (4.3°  to  5.2°  F),  depending  on  which  model  is  used  to  derive 
the  estimated  temperature  change. 

Based  on  one  climate  model  in  which  the  hydrologic  cycle  is  modeled 
in  detail  along  with  other  aspects  of  climate  behavior,  a  doubling  of 
carbon  dioxide  has  been  calculated  to  result  in  about  a  7  percent  increase 

41Bolin,  Bert.  "Changes  of  Land  Biota  and  Their  Importance  for  the  Carbon  Cycle  ;  The 
Increase  of  Atmospheric  Carbon  Dioxide  Mav  Partlv  Be  Due  to  the  Expansion  of  Forestry 
and  Agriculture."  Science,  vol.  196,  May  6.  1977.  pp.  613-615. 

"2  Siegreuthalpr.  U  and  H.  Oeschsrpr.  "Predicting  Future  Atmospheric  Carbon  Dioxide 
Levels."  Science,  vol.  199,  Jan.  27,  1978,  pp.  388-395. 

43WooriwHl.  Geo-cre  M.,  "The  Carbon  Dioxide  Question,"  Scientific  American,  vol.  238, 
Janvary  1978.  pp.  34-43. 

44  National  Research  Council.  Geophysics  Research  Board,  "Energy  and  Climate,"  Wash- 
ington, National  Academy  of  Sciences,  1977,  281  pp. 


in  global  average  precipitation.  Most  of  this  increase  would  be  con- 
centrated in  higher  latitudes.  A  general  retreat  of  snow  and  sea  ice 
cover,  by  perhaps  as  much  as  10  degrees  of  latitude,  could  result  in 
the  Arctic  regions.  The  extent  of  such  changes  in  the  Antarctic,  how- 
ever, has  not  been  determined.  The  temperature  rise  is  greater  by  a 
factor  of  three  or  four  in  polar  regions  than  the  average  temperature 
change  for  the  world  as  a  whole.  For  each  further  doubling  of  carbon 
dioxide,  an  additional  3°  C  increase  in  air  temperature  is  inferred.  This 
would  mean  that  should  the  carbon  dioxide  concentration  approach 
four  to  eight  times  preindustrial  levels,  and  increase  in  global  mean  air 
temperature  of  more  than  6°  C  (11°  F)  could  be  realized — at  which 
time  Earth  would  be  experiencing  temperatures  warmer  than  those  at 
any  time  in  the  last  million  years.45 

Implications  of  a  climatic  warming 

The  implications  for  man-induced  climatic  warming  are  particularly 
far-reaching  for  agriculture,  according  to  the  NRC  report.  The  global 
picture  presented  by  the  report  is  one  dominated  by  the  f orementioned 
gradual  increase  in  mean  air  temperatures,  with  a  concomitant  shift- 
ing of  agricultural  zones,  altered  rainfall  patterns  and  other  major 
changes.  Worldwide  average  annual  precipitation  could  increase, 
which,  at  first  glance,  would  seem  to  benefit  agriculture.  The  accom- 
panying higher  air  temperature,  however,  would  raise  the  rate  of 
evapotranspiration  from  cultivated  lands,  and  part  of  the  benefits 
from  the  additional  water  supply  could  be  lost.  In  some  regions, 
evapotranspiration  might  exceed  the  increase  in  precipitation;  in 
others,  the  reverse  might  be  true.  At  higher  latitudes,  there  would  be 
a  longer  frostf ree  growing  season  than  at  present,  and  the  boundaries 
of  cultivation  could  be  extended  northward  in  the  Northern  Hemi- 
sphere. Attendantly,  summer  temperatures  might  become  too  high  for 
full  production  of  middle-latitude  crops  such  as  corn  and  soy  beans 
grown  in  Iowa,  Illinois,  Indiana,  and  Missouri,  and  it  might  be 
necessary  to  shift  the  Corn  Belt  toward  the  north  where  less  produc- 
tive soils  are  encountered.  Generally  speaking,  warmer  temperatures 
would  result  in  a  poleward  movement  of  agroclimatic  zones.  As  the 
authors  of  the  NRC  report  state : 

The  most  serious  effects  on  agriculture  would  arise  not  from  changes  in  global 
average  conditions  but  from  shifts  in  the  location  of  climatic  regions  and  changes 
in  the  relationships  of  temperature,  evapotranspiration,  water  supply,  cloudi- 
ness, and  radiation  balance  within  regions.  Present  cropping  patterns,  crop  vari- 
eties, and  farming  technology  in  different  climatic  regions  are  based  on  cumula- 
tive experience  over  many  years  in  the  selection  of  appropriate  crop  species  and 
varieties  for  each  region  and  in  adapting  both  the  plants  and  their  physical 
environment  to  each  other  in  as  nearly  an  optimal  fashion  as  possible.  These 
adaptations  have  remained  fairly  satisfactory  over  the  relatively  nam  nge 
of  climatic  changes  that  have  occurred  in  the  historic  past.  But  large  el  in 
climatic  relationships  within  regions  such  as  might  be  brought  abo  a 
doubling  or  quadrupling  of  atmospheric  carbon  dioxide  would  almost  c  _ily 
exceed  the  adaptive  capacity  of  crop  varieties  grown  at  present.46 

The  potential  global  warming  trend  associated  with  increasing  con- 
centrations of  atmospheric  carbon  dioxide  could  increase  desertifica- 
tion,47 although  there  is  not  conclusive  evidence  for  this  possibility. 

*Mbid.,  pp.  4,  5. 

47  The  awkward  word  "desertification"  often  refers  to  the  process  by  which  existing  deserts 
spread  but  the  term  also  may  refer  to  the  creation  of  desertlike  conditions  such  as  those 
which  developed  during  the  1930's  dust-bowl  years  in  the  North  American  Great  Plains. 


The  altered  pattern  of  rainfall  and  temperature  resulting  from  the 
release  of  carbon  dioxide  could  change  desert  conditions  in  unexpected 
ways  and  even  increase  agricultural  potential  in  some  cases.  Authors 
of  the  NRC  report  concede  the  present  state  of  ignorance  on  the 
subject : 

The  most  serious  effects  of  possible  future  climatic  changes  could  be  felt  along 
the  boundaries  of  the  arid  and  semiarid  regions  in  both  hemispheres.  We  need  to 
be  able  to  estimate  whether  these  belts  of  aridity  and  semiaridity  will  move 
toward  or  away  from  the  poles  and  whether  they  will  expand  or  contract  in 

The  effect  of  manmade  or  of  natural  climatic  alteration  of  desert- 
areas  is  not  clear.  The  advancement  of  desert  conditions  into  agri- 
cultural areas  in  Africa  and  elsewhere  has  been  documented  during 
the  past  decade,  and  although  rainfall  patterns  with  associated  wet 
and  dry  climates  are  controlled  mainly  by  the  general  atmospheric 
circulation,  human  activities  can  have  a  marked  effect  on  local  desert 
conditions,  even  possibly  intensifying  the  process  of  desertification  and 
thereby  compounding  the  problem.  In  particular,  excessive  ploughing 
of  dry  land  or  overenthusiastic  introduction  of  livestock  and  expan- 
sion of  cultivated  areas,  during  wet  periods,  into  marginal  lands  causes 
destruction  of  soil-protecting  vegetation.  During  ensuing  dry  periods, 
these  marginal  lands,  with  their  natural  protective  cover  destroyed  by 
cultivation  and  overgrazing,  suffer  loss  of,  or  a  decline  in,  the  quality 
of  soil.  As  this  occurs  over  a  large  region,  the  bare  dry  ground,  its 
reflectivity  altered,  now  acts  to  intensify  the  natural  climatic  condi- 
tions which  sustain  the  desert.49 

Carbon  dioxide  and  future  climate:  the  real  climate  versus  "model 

In  the  final  analysis,  it  is  well  to  remember  that  it  cannot  be  asserted 
that  a  doubling  of  carbon  dioxide  in  the  real  world  would  have  the 
same  effects  on  real  climate  as  a  simulated  doubling  of  carbon  dioxide 
in  climate  models  would  have  on  "model  climate."  This  caveat  is  in 
order  because  no  climate  model  is  altogether  realistic  in  its  description 
of  the  real  climatic  system,  and  because  some  of  the  physical  processes 
that  operate  in  the  real  climatic  system  cannot  yet  be  simulated  at  all 
in  climate  models.  Comments  J.  Murray  Mitchell,  Jr. : 

No  climate  model  on  which  the  above  conclusions  [regarding  climatic  warm- 
ing] are  based  is  capable  of  developing  its  own  cloud  systems  in  a  realistic 
way :  most  models  must  be  instructed  before  hand  where  the  clouds  are  assumed 
to  exist,  and  the  clouds  remain  there  unchanged  throughout  the  computer 
experiment  using  the  model.  We  should  be  wary  of  this,  because  if  the  cloudi- 
ness were  to  change  in  the  real  world  along  with  a  carbon  dioxide  change, 
then  the  role  of  clouds  in  affecting  the  temperature  of  the  Earth  might  sig- 
nificantly alter  the  net  temperature  effect  of  the  carbon  dioxide  change  as 
inferred  from  models  that  assume  fixed  cloudiness.50 

the  model  is  allowed  to  adjust  cloudiness  along  with  other  weather 
variables  as  the  calculation  proceeds.  Early  indications  are  that 
Some  preliminary  model  experiments  have  been  attempted  at  the 
National  Oceanic  and  Atmospheric  Administration's  (NOAA)  Geo- 
physical Fluid  Dynamics  Laboratory  in  Princeton,  N.J.,  in  which 

48  National  Research  Council,  Geophysics  Research  Board,  op.  cit.,  p.  14. 
48  Ibid. 

50  Mitchell,  J.  Murray,  Jr.,  "Carbon  Dioxide  and  Future  Climate,"  p.  9. 


allowance  for  cloudiness  changes  does  not  greatly  alter  the  results  of 
experiments  using  models  with  fixed  cloudiness. 

Altogether,  the  experience  with  climate  models  suggests  that  their 
use  in  evaluating  the  magnitude  of  temperature  changes  associated 
with  changes  of  atmospheric  carbon  dioxide  leads  to  results  that  are 
likely  to  approximate  reality  fairly  closely.  Models  may  be  overesti- 
mating the  temperature  and  other  climatic  effects  of  carbon  dioxide 
changes  by  as  much  as  a  factor  of  two.  On  the  other  hand,  it  is 
equally  likely  that  they  may  be  underestimating  the  effects  by  a 
factor  of  two.  In  balance,  the  model  results  to  date  warrant  being 
taken  as  an  unprejudiced  and  credibly  realistic  approximation  to 


The  concern  that  man's  activities  could  in  some  fashion  change  the 
stratosphere  first  emerged  as  a  public  issue  during  the  debate  on  the 
American  SST  in  1969.  The  American  SST  program  was,  at  that 
time,  almost  a  decade  old  and  was  approaching  its  final  phase  when 
it  was  challenged  by  a  coalition  of  more  than  30  environmentally 
oriented  organizations.  The  environmentalists  contended  that  the 
SST,  flying  in  the  stratosphere,  would  contaminate  the  stratosphere 
and  alter  its  characteristics.  The  dominant  concern  was  that  water, 
created  as  a  product  of  fuel  combustion,  would  interact  with  the 
stratospheric  ozone  and  destroy  it. 

Concerns  regarding  ozone  destruction 

Ozone  (03)  exists  everywhere  in  the  atmosphere  and  reaches  a 
maximum  concentration  at  around  80,000  feet.  It  is  created,  as  well 
as  destroyed,  by  the  interaction  of  ultraviolet  light  from  the  Sun  with 
oxygen  molecules  in  the  upper  atmosphere.  Most  of  the  ozone  is 
created  in  the  Tropics  and  is  dispersed  from  there  toward  both  poles. 
Due  to  the  destructive  action  of  sunlight  and  to  the  atmospheric 
transport  systems,  the  Tropics,  where  most  of  the  ozone  is  made,  have 
the  least  dense  coverage  of  ozone.  Ozone  density  increases  in  the 
temperate  zones  and  reaches  its  maximum  density  in  the  polar  regions. 
Ozone  density  over  a  given  spot  on  Earth  may  vary  as  much  as  25 
to  30  percent  on  a  given  day  and  as  much  as  300  percent  throughout 
the  year  depending  on  the  season.  Ozone  density  measurements  have 
shown  that  the  Northern  Hemisphere  of  the  Earth  has  a  slightly 
denser  coverage  than  the  Southern  Hemisphere. 

The  importance  of  the  ozone  content  of  the  upper  atmosphere 
centers  on  the  fact  that  the  ultraviolet  light  that  creates  ozone  is 
absorbed  in  the  process.  These  wavelengths  of  ultraviolet  light  are 
damaging  to  life  of  all  sorts  if  the  intensity  is  too  great.  It  should  be 
noted  that  some  ultraviolet  light  is  required  by  animal  life  to  produce 
vitamin  D  which  gives  protection  against  rickets. 

In  the  debate  over  the  American  SST,  it  became  clear  that  neither 
side  had  enough  data  on  the  stratosphere  to  refute  the  other.  Despite 
this,  the  debate  remained  lively  for  more  than  a  year  and  was  finally 
terminated  by  the  congressional  decision  to  cancel  the  SST  program 
and  to  initiate  programs  to  study  the  upper  atmosphere  and  in  par- 
ticular, its  ozone. 

51  Information  gleaned  In  a  session  on  "climatic  futures"  at  the  1978  annual  meeting  of 
the  American  Association  for  the  Advancement  of  Science  in  Washington,  D.C.,  Feb.  17, 


Congress  requested  and  funded  a  3-year,  $24  million  program,  to 
determine  whether  or  not  the  stratospheric  flight  constituted  a  threat 
to  the  Earth's  environment.  Responsibility  for  the  study  was  given  to 
the  Department  of  Transportation  and  was  called  the  "Climatic  Im- 
pact Assessment  Program"  (CIAP).52  The  theoretical  mechanisms 
which  indicated  that  water,  created  from  the  combustion  of  fuel,  would 
mix  with  and  destroy  ozone  appeared  to  be  reasonable  and  meritorious 
of  serious  study.  Early  in  the  CIAP,  however,  actual  measurements  of 
ozone  density  in  the  stratosphere  in  volumes  of  air  which  were  per- 
meated by  the  plume  from  jet  engines,  were  made.  These  measurements 
showed  that  ozone  density  seemed  to  increase  subsequent  to  the  injec- 
tion of  water  vapor.  Why  this  occurs  is  not  yet  understood,  but  the  test 
provided  adequate  information  to  conclude  that  water  vapor  injected 
into  the  stratosphere  would  not  constitute  a  danger  to  the  ozone. 

During  the  conduct  of  the  CIAP  program,  other  papers  began  to 
appear  which  described  a  variety  of  heretofore  unconsidered  theoreti- 
cal ways  in  which  man's  activities  could  adversely  effect  the  ozone 
density  in  the  stratosphere.  The  atmosphere  of  the  Earth  is  about  80 
percent  nitrogen  and  20  percent  oxygen.  The  oxygen  used  in  the  com- 
bustion process  is  therefore  accompanied  by  a  large  amount  of  nitro- 
gen. The  heat  of  combustion  causes  the  formation  of  several  oxides  of 
nitrogen  (NOx).  Theoretical  mechanisms  were  proposed  which  pre- 
dicted that  the  NOx  formed  in  the  stratosphere  by  a  jet  engine  would 
mix  with  the  ozone  and  destroy  it  in  a  catalytic  manner.  In  other 
words,  during  the  process  in  which  the  NOx  would  destroy  the  ozone, 
the  XOx  would  be  reformed  and  released  to  destroy  still  more  ozone 
in  a  continuous  manner.53  The  mechanisms  for  this  process  appeared 
reasonable  and  worthy  of  serious  study.  However,  Dr.  John  J. 
McKetta  of  the  CEQ  noted  that  the  total  NOx  burden  produced  by 
combustion  processes  amounts  to  only  about  2  percent  of  that  produced 
by  dying  vegetation  in  the  natural  cycle  of  plant  life.54  It  was  then 
noted  that  the  artificial  insertion  of  nitrogen  compounds  into  the  soil 
for  purposes  of  fertilizing  caused  the  evolution  and  ultimate  release 
of  XOx  in  quantities  amounting  to  a  sizable  fraction  of  that  produced 
by  nature. 55 • 56 

Moreover  the  bromine  compounds  used  in  agriculture  as  antifungi- 
cides  were  held  to  be  even  more  potent  in  destroying  ozone  than  NOx.57 
Still  more  very  large  sources  of  NOx  were  identified,  such  as  lightning 
from  the  some  5.000  storms  around  the  Earth,  each  day.  Also,  air 
bursts  of  nuclear  bombs  produce  NOx  at  the  rate  of  10,000  tons  per 
megaton  of  yield.  58, 59  In  the  early  1960?s,  340  megatons  of  explosive 
injected  about  3%  million  tons  of  XOx  into  the  stratosphere. 

52  "Climatic  Impact  Assessment  Program  Development  and  Accomplishments,  1971-75," 
J.  Mormino,  et  al.,  D0T-TST-76-41,  December  1975. 

53  "Reduction  of  Stratospheric  Ozone  by  Nitrogen  Oxide  Catalysts  from  Supersonic  Trans- 
port Exhaust,"  H.  Johnston,  Science,  Aug.  6,  1971. 

54  "The  Eight  Surprises,"  J.  J.  McKetta.  address  to  the  American  Trucking  Association, 
Oct.  16.  1974.  reprinted  in  the  Congressional  Record.  Mar.  12,  1975. 

55  "NOAA  Scientist  Weighs  Possible  Fertilizer  Effects  on  Ozone,"  Paul  Crutzen,  Depart* 
ment  of  Commerce  News,  Apr.  15,  1975. 

56  "Nitrogen  Fertilizer  Threatens  Ozone,"  quotes  from  J.  McElroy,  Washington  Star, 
Dec.  12.  1974. 

57  "Weather  Warfare"  (Bromine).  New  Scientist,  Mar.  27,  1975,  p.  762. 

58  "Ozone  Appears  Unalterpd  by  Nitric  Oxide,"  Kenneth  J.  Stein,  Aviation  Week  and  Space 
Technology,  Nov.  6,  1972.  p.  28.  •  •  .    ^        ,r  , 

.  59  "Nitrogen  Oxides,  Nuclear  Weapon  Testing,  Concorde  and  Stratospheric  Ozone,"  P. 
Goldsmith,  et  at,  Nature,  Aug.  31,  1973,  p.  545. 

34-857—79  14 


It  had  begun  to  appear  to  many  that,  in  the  Earth's  atmosphere, 
which'  is  about  80  percent  nitrogen  and  20  percent  oxygen,  the  NOx  is 
ubiquitous  and  that  there  was  just  no  legislative  way  to  save  the  ozone 
from  the  catalytic  disintegration  hypothesized.  The  issue  endures 
largely  as  an  academic  debate,  though  its  character  could  change  again. 
One  group  holds  that  the  destructive  mechanisms  ascribed  to  NOx  are 
real  and  that  ozone  density  is  controlled  by  the  presence  of  NOx-  An 
opposing  group  contends  that,  while  the  hypothetical  reactions  appear 
to  be  sound,  they  just  don't  seem  to  occur.  The  insertion  of  3%  million 
tons  of  XOx  by  nuclear  explosions  over  1  year's  time,  for  example,  was 
judged  by  many  as  an  experiment  of  sufficient  magnitude  to  cause  un- 
mistakable perturbations  in  ozone  density,  and  would  prove  or  dis- 
prove the  destruction  hypothesis.  Recordings  of  ozone  density  before, 
during,  and  following  the  test  were  analyzed  by  numerous  people.  One 
investigator  detected  trends  which  he  associated  with  the  explosions ; 
however,  others  held  that  "the  conclusion  that  massive  injections  of 
nitrogen  oxides  into  the  stratosphere  do  not  upset  the  ozone  layer  seems 
inescapable."  60 

Putting  that  aside,  yet  another  challenge  to  the  ozone,  the  manmade 
fluorocarbons  (freon  aerosol  propellants  and  refrigerants)  has  been 
postulated.61  The  hypothetical  mechanisms  by  which  these  compounds 
would  migrate  into  the  stratosphere,  break  down  to  release  odd  chlorine 
molecules  which  would  in  turn  set  up  a  catalytic  destruction  of  ozone, 
where  examined  and  found  to  be  plausible  and  a  cause  for  concern.  Sub- 
sequent measurements  taken  in  the  stratosphere  proved  the  presence  of 
numerous  odd  chlorine  molecules,  some  of  which  could  indeed  be  shown 
to  have  their  origin  in  freon.62 

Although  the  empirical  validity  of  the  destructive  interaction  of 
these  odd  chlorines  with  ozone  is  difficult  to  show  and  has  yet  to  be 
shown,  their  discovery  in  the  stratosphere  was  enough  for  several 
scientists  to  call  for  a  ban  on  the  fluorocarbons.  Other  scientists,  as  well 
as  industry,  took  an  opposing  view,  calling  for  empirical  proof  prior  to 
taking  actions  to  ban  or  control  the  manufacture  or  use  of  freon 

The  argument  became  partly  one  of  timing  with  one  side  claiming 
that  no  emergency  could  be  proven  and  plenty  of  time  was  available  to 
test  the  destruction  hypothesis.  Opposing  this  was  the  view  that  it  may 
very  well  be  too  late  already  since  most  of  the  freons  already  released 
have  yet  to  reach  the  stratosphere. 

Unlike  the  case  with  XOx.  where  changes  as  vast  as  banning  the 
use  of  nitrating  fertilizers  might  be  required,  the  control  of  freon 
release  was  a  manageable  target  for  a  regulatory  control.  The  resulting 
studies  and  actions  represent  a  model  of  rapid  and  cooperative  action 
between  a  large  number  of  highly  diverse  Government  offices  and 
agencies.  The  decision  was  made  to  act  without  waiting  for  empiricial 
proof  of  the  destruction  hypothesis,  but  not  to  institute  the  total  and 
immediate  ban  some  investigators  called  for.  Instead,  propellant  ap- 
plication would  be  labeled  as  possibly  hazardous  to  the  ozone  and  then 

"°  I '»id. 

r;  "Stratospheric  O^one  Destruction  hv  Man-made  Ohlorofluoromethanes,"  R.  J.  Cicerone, 
et  al..  Science,  Sept.  27,  1974. 

""Atmospheric  Halocarbons  and  Stratospheric  Ozone,"  J.  E.  Lovelock,  Nature,  Nov.  22, 


i banned  in  stages.  Refrigerants  would  be  studied  pending  their  possible 
regulation  at  some  future  time. 

Action  by  the  Government  on  the  regulation  of  fluorocarbons 

The  Council  on  Environmental  Quality  (CEQ)  and  the  Federal 
Council  for  Science  and  Technology  (FCST)  reviewed  theoretical 
oapers  on  the  destructive  interaction  between  fluorocarbons  and  ozone, 
the  first  of  which  appeared  in  1974.  They  decided  that  the  case  was 
worthy  of  serious  concern.  In  January  1975,  the  CEQ  and  FCST 
jointly  created  a  large  ad  hoc  task  force  known  as  the  Federal  Inter- 
agency Task  Force  on  Inadvertent  Modification  of  the  Stratosphere 
(IMOS).  IMOS  membership  included  representatives  from: 

Interdepartmental  Committee  for  Atmospheric  Sciences  (ICAS). 

Department  of  Agriculture. 

Department  of  Commerce, 

Department  of  Defense. 

National  Institute  of  Environmental  Health  Sciences. 

Food  and  Drug  Administration. 

Department  of  Justice. 

Department  of  State. 

Department  of  Transportation. 

Energy  Research  and  Development  Administration. 

Environmental  Protection  Agency. 

Consumer  Products  Safety  Commission. 

National  Aeronautics  and  Space  Administration. 

National  Science  Foundation. 

Council  on  Environmental  Quality. 

Office  of  Management  and  Budget  (observer  only) . 

The  work  of  IMOS  was  swift  and  orderly.  A  series  of  studies  was 
completed  and  published  in  their  report  by  June  1975.63  IMOS  con- 
cluded "that  fluorocarbons  released  to  the  environment  are  a  legitimate 
cause  for  concern."  The  report  also  referred  to  a  similar  study  which 
was  then  underway  at  the  National  Academy  of  Sciences.  IMOS  rec- 
ommended that,  should  the  results  of  the  NAS  study  agree  with  their 
results,  then  Federal  regulatory  agencies  should  initiate  rulemaking 
procedures  for  implementing  regulations  to  restrict  fluorocarbon  uses. 

The  data  base  for  the  NAS  study  was  of  course  the  same  data  base 
used  by  IMOS  since  it  was  the  only  one  available.  The  conclusions 
reached  by  both  studies  were  therefore  the  same,  and  rulemaking  was 

If  the  data  base  could  have  contained  some  empirical  proof  sup- 
porting the  validity  of  the  massive  ozone  destruction  hypothesis,  the 
rulemaking  procedures  would  have  proceeded  without,  or  at  least  with 
much  less  debate  and  protest.  As  it  was,  the  rules  were  handed  down 
without  proof,  the  justification  being  that  the  consequences  of  higher 
UV  exposure  due  to  ozone  thinning  were  sufficiently  severe  that  pre- 
cautionary regulations  were  necessary.  Under  these  circumstances,  the 
rules  Ave  re  models  of  compromise.  A  ban  was  to  be  issued  over  the  pro- 
test of  industry,  but  it  would  neither  be  the  complete  ban  nor  the  imme- 
diate one  demanded  by  the  environmental  groups  and  some  scientists. 

63  '"Fluorocarbons  and  the  Environment,"  IMOS.  Council  on  Environmental  Quality  and 
the  Federal  Council  for  Science  and  Technology,  June  1975. 


The  proposed  rules  were  formulated  jointly  by  the  Department  of 
Health,  Education,  and  Welfare,  the  Environmental  Protection 
Agency,  and  the  Consumer  Product  Safety  Commission.  In  brief,  they 

state : 

1.  By  October  15,  1978,  no  company  may  manufacture  fluoro- 
carbons  for  use  in  aerosol  products. 

2.  By  December  15, 1978,  companies  must  stop  using  fluorocar- 
bons  as  propellants  in  aerosol  products. 

3.  As  of  April  15,  1979,  no  spray  product  containing  a  fluoro- 
carbon  propellant  may  be  introduced  into  interstate  commerce. 
Products  on  store  shelves  at  that  time  may  be  sold,  however,  and 
there  will  be  no  recall. 

4.  Beginning  in  October  1978,  warning  labels  will  be  put  on 
aerosol  products  which  contain  fluorocarbons  to  warn  the  user 
that  the  fluorocarbons  are  present  and  may  affect  the  ozone. 

5.  Certain  aerosol  products  intended  for  medical  purposes  are 
exempt  from  these  regulations. 

The  rule  on  labeling  has  already  been  put  into  effect.64 

Climatic  effects  of  ozone  depletion 

While  the  effect  of  a  significant  buildup  in  the  concentration  of 
chlorofluorocarbons  and  chlorocarbons  on  the  chemical  balance  of  the 
Earth/atmosphere  system  is  currently  a  subject  of  concern,  their  im- 
pact and  effect  on  the  Earth's  overall  thermal  energy  balance  must 
also  be  considered.  The  chlorofluorocarbons  and  chlorocarbons  have 
strong  infrared  absorption  bands,  thus  allowing  these  compounds  to 
trap  long-wave  radiation  emitted  by  the  Earth  and,  in  turn,  enhance 
the  atmospheric  "greenhouse  effect."  This  enhancement  may  lead  to 
an  appreciable  increase  in  global  surface  and  atmospheric  temperature 
if  atmospheric  concentrations  of  these  compounds  reach  values  of  the 
order  of  2  parts  per  billion  (ppb)  ,65 

Furthermore,  ozone  itself  is  important  to  the  Earth's  climate  because 
it  absorbs  some  quantities  of  both  solar  and  terrestrial  infrared  radia- 
tion, thereby  affecting  the  enerofv  balance  of  the  Earth/atmosphere 
system  that  determines  the  Earth's  temperature.  Exactly  how  changes 
in  the  ozone  concentration  might  affect  climate  are  far  more  difficult 
to  determine,  since  changes  in  surface  temperature  from  variations  in 
ozone  depend  on  such  diverse  factors  as  whether  the  total  amount  of 
ozone  is  increased  or  decreased,  whether  the  height  at  which  the  maxi- 
mum amount  of  ozone  occurs  is  altered,  or  whether  the  latitudinal 
distribution  of  ozone  is  disturbed.  James  Coakley  of  the  National  Cen- 
ter for  Atmospheric  Research  (NCAR),  Boulder,  Colo.,  has  found 
that  a  uniform  reduction  in  the  total  amount  of  atmospheric  ozone 
would  lead  to  a  cooling  of  the  Earth's  surface,  but  that  a  decrease  in 
altitude  in  the  stratosphere  where  ozone  has  its  maximum  concentra- 
tion can  warm  the  surface.  Similarly,  an  increase  in  total  amount  of 
ozouo  warms,  but  an  increase  in  the  altitude  of  maximum  ozone  con- 
centration can  cool  the  climate.  If  it  were  known  that  an  atmospheric 

«  The  previous  section  on  the  ozone  depletion  Issue  was  contributed  by  George  Chatham, 
Spprinllst  In  Aeronautics  and  Space,  Science  Policy  Research  Division,  Congressional  Re- 
peareh  Service. 

* Rnmanathan.  V.,  "Greenhousp  Effect  Due  to  Chlorofluorocarbons:  Climatic  Implica- 
tions" Science,  vol.  190,  Oct.  3,  1975,  pp.  50,  51. 


pollutant,  such  as  chlorofluorocarbons,  acted  to  reduce  the  amount  of 
ozone  in  the  atmosphere,  then  before  one  could  conclude  that  this  would 
lead  to  a  global  cooling,  it  would  still  also  have  to  be  known  if  the 
clilorofluorocarbons  moved  the  altitude  of  maximum  ozone  concen- 
tration up  or  down.  If  the  maximum  moved  up,  this  would  enhance 
the  cooling  effect  of  a  decrease  in  ozone,  but  if  the  maximum  moved 
down,  that  situation  would  oppose  the  cooling  attributable  to  the 
decrease  in  total  ozone.  Thus,  while  it  is  conceivable  that  a  large  change 
in  ozone  could  significantly  affect  climate,  it  may  be  seen  that  the 
direction  of  any  potential  ozone-climatic  effect  is  difficult  to  deter- 


Another  man-generated  pollutant  that  could  affect  the  climate  is 
waste  heat  generated  by  combustion,  automobiles,  home  heating,  in- 
dustrial processes,  and  power  generation — all  produce  heat  that  even- 
tually is  emitted  into  the  atmosphere.  In  addition  to  its  direct  effect 
on  atmospheric  temperature,  in  specific  situations  waste  heat  can  en- 
hance convection,  the  vertical  motion  so  important  in  precipitation 

On  a  regional  scale,  thermal  effects  may  become  important  by  the 
turn  of  the  century.  However,  on  a  global  scale,  climatic  effects  of 
thermal  pollution  today  and  for  the  near  future  appear  to  be  insig- 
nificant. Some  scientists,  however,  believe  this  impact  may  grow  with 
increased  energy  production  and  conversion.  Research  meteorologist 
James  T.  Peterson  of  the  Environmental  Protection  Agency  states 
that  a  long-term  view  reveals  that  continued  growth  of  energy  use 
could  lead  to  a  large-scale  climatic  change  in  100  years  or  more.  Of 
particular  concern,  says  Peterson,  are  present-day  nuclear  power- 
plants,  which  will  produce  about  55  percent  more  waste  heat  than  a 
fossil  fuel  plant  for  a  given  amount  of  electricity  generated.67 

To  better  understand  the  effects  of  heat  releases  on  weather  and 
climate,  the  U.S.  Department  of  Energy  is  sponsoring  a  program  called 
METER,  which  stands  for  "meteorological  effects  of  thermal  energy 
releases."  METER  program  scientists  are  collecting  data  from  several 
powerplant  sites  around  the  United  States  to  aid  in  predicting  the 
specific  environmental  effects  of  releasing  large  amounts  of  excess  heat 
and  moisture  directly  into  the  atmosphere  from  powerplant  operations 
and  cooling  towers.  The  amounts  of  heat  and  moisture  emitted  from 
the  stacks  and  towers  of  a  large  powerplant  are  small  compared  with 
those  released  by  even  a  moderate-sized  thunderstorm.  Cooling  tower 
plumes  are  suspected  of  acting  as  a  triggering  mechanism  to  create 
instabilities  in  the  atmosphere,  initiating  or  otherwise  modifying 
rainfall  and  disrupting  storm  patterns.  A  typical  cooling  tower  will 
produce  5,000  megawatts  of  heat  and  evaporate  40,000  to  60,000 
gallons  of  water  per  minute.  Even  so,  a  modest  thunderstorm  will  put 
out  800  times  that  much  water  and  30  times  that  much  heat.68 

The  urban  "heat  island" 

•  On  a  local  scale,  the  climatic  effects  of  energy  use  and  heat  produc- 
tion are  significant  and  well  documented.  Obviously,  urban  areas  are 

66  Schneider.  Stephen  H.,  "The  Genesis  Strategy:  Climate  and  Global  Survival."  New 
York.  Plenum  Press,  1976.  p.  183. 

67  Peterson,  James  T.,  "Energy  and  the  Weather,"  Environment,  vol.  15,  October  1973, 
PP.  4,  5,  8. 

88  "Power  Plant  May  Alter  Weather,"  the  Christian  Science  Monitor,  Mar.  13,  1978,  p.  19. 


experiencing  thermal  effects.  The  most  evident  feature  of  city  climate 
is  its  excess  warmth,  which  is  commonly  referred  to  as  the  urban  heat 
island.  Cities  are  prodigious  sources  of  heat.  Factory  smokestacks,  air- 
conditioners  and  heating  systems  of  offices  and  homes,  vehicle  engines 
and  exhausts — all  contribute  waste  heat  to  the  outside  atmosphere', 
particularly  in  winter.  Summer  temperatures  in  the  city  are  0.6°  C  to 
1.1°  C  higher  than  in  nearby  rural  areas,  and  1.1°  C  to  2.2°  C  higher  in 
winter.  Also,  the  building  materials  of  brick,  asphalt,  mortar,  and 
concrete  readily  absorb  and  store  more  heat  from  the  Sun  than  the  soil 
and  vegetation  of  a  rural  area,  and  give  it  up  more  slowly  after  sun- 
down. While  rural  areas  are  rapidly  cooling  after  sunset,  the  building 
materials  gradually  release  their  stored  heat  to  the  urban  atmosphere, 
tending  to  keep  it  warmer  than  the  countryside. 

Another  factor  that  retains  high  temperatures  and  makes  the  atmos- 
phere dry  is  the  way  a  city  disposes  of  its  rainwater  or  snow.  During 
any  shower  or  storm,  the  water  is  quickly  drained  from  the  roofs  by 
gutters  and  drainpipes,  and  from  the  sidewalks  and  streets  by  gutters 
and  storm  sewers.  The  winter  snows  are  removed  as  quickly  as  possible 
by  shovels  and  plows,  and  often  hauled  away  in  trucks.  These  methods 
of  removing  precipitation  not  only  take  away  sources  of  moisture  but 
also  remove  the  cooling  effect  of  evaporation.  In  the  country,  evapora- 
tion can  cool  the  area  where  the  rain  and  melting  snow  stay  on  the 
surface  or  seep  into  the  ground.  A  large  fraction  of  the  absorbed  heat 
energy  is  used  in  evapotranspiration  as  vegetation  transpires  water 

An  advantage  of  urban  heat  emissions  is  that  the}7  decrease  the 
likelihood  of  surface-based  air  temperature  inversions  (air  tempera- 
ture increases  rather  than  decreases  with  height)  and  increase  the 
height  of  the  mixed  layer  near  the  surface.  Inversions  inhibit  turbu- 
lent air  motions  which  diffuse  and  dilute  pollutants.  Heat  emissions  at 
the  city  surface  create  a  relative  decrease  in  temperature  with  height 
which  in  turn  aids  the  mixing  and  dispersion  of  pollutants.  Observa- 
tions of  urban  and  rural  temperature-height  profiles  have  shown  this 
effect  of  thermal  emissions.  Thus,  urban  pollutants  emitted  near 
ground  level,  such  as  carbon  monoxide  from  auto  exhaust,  will  be 
diffused  through  a  greater  volume  of  the  atmosphere  with  a  consequent 
reduction  in  concentration. 

Other  major  features  of  urban  climates  that  are  related  to  thermal 
pollution  include : 

A  longer  frost-free  growing  season. 

Less  snowfall  because  snow  melts  while  falling  through  the 
warmer  urban  atmosphere  and  less  snow  accumulation  because 
-now  melts  on  contact  with  warmer  urban  surfaces. 

Lower  relative  humidity. 

Decreased  occurrence  and  density  of  fog  because  of  the  lower 
relative  humidity,  a  feature  which  may  be  offset  by  more  par- 
t  Iculate  matter  which  serves  as  condensation  nuclei. 

A  slight  component  of  the  wind  direction  toward  the  city  cen- 
ter as  a  result  of  the  horizontal  temperature  contrast. 

Apparent  enhancement  of  precipitation  downwind  of  cities,  a 
phenomenon  partially  due  to  increased  convection  (vertical 



The  calbedo  is  a  numerical  indication  of  the  percentage  of  incoming 
i>lar  radiation  that  is  reflected  by  the  land,  ocean,  and  atmosphere  back 
into  space  and,  attendantly,  how  much  is  absorbed  by  the  climatic  sys- 
tem. Another  important  manner  for  altering  the  Earth's  heat  budget, 
albedo  can  be  changed  by  the  process  of  urbanization,  agricultural 
activities,  changes  in  the  character  of  the  land  surface,  and  by  in- 
creasing or  decreasing  cloudiness.69 

Most  clouds  are  both  excellent  absorbers  of  infrared  radiation  and 
rellectors  of  solar  radiation.  Therefore,  clouds  are  a  major  factor  in 
determining  the  Earth's  energy  balance.  An  increase  in  clouds  could 
warm  surface  temperatures  by  tending  to  reduce  the  flux  of  long- wave 
(that  is,  infrared)  radiation  to  space,  or  cool  surface  temperatures  by 
reflecting  incoming  solar  radiation  back  to  space.  The  net  effect  of 
increased  cloudiness  is  to  either  warm  or  cool  the  surface,  depending 
on  cloud  type,  latitude,  and  season.70  The  effect  of  cloud  condensation 
nuclei  (CCN)  on  the  formation  of  fog  and  clouds  could  alter  the  albedo 
of  a  region  if  the  fog  or  clouds  were  sufficiently  persistent  or  extensive, 
P.  V.  Hobbs  and  H.  Harrison,  both  professors  of  atmospheric  science 
at  the  University  of  Washington,  and  E.  Eobinson  of  Washington 
State  Universit3T?s  Air  Pollution  Research  Unit,  contend  that  perhaps 
the  most  sensitive  atmospheric  processes  which  can  be  affected  by  air 
pollutants  are  those  involved  in  the  development  of  clouds  and  pre- 

Apart  from  effects  on  precipitation  processes,  inadvertent  modifi- 
cation of  the  microstrncture  and  distribution  of  clouds,  with  attend- 
ant consequences  for  radiative  properties,  could  have  profound  effects 
on  atmospheric  temperature  distributions  and  global  climate.71 
Whether  a  variation  in  terrain  on  temperature  or  other  factors  would 
have  a  negative  or  positive  feedback  interaction  with  clouds  is  a 
major  question  in  climate  theory  that  will  be  answered  by  extensive 
analyses  of  observations  and  model  studies. 

The  high  reflectivity  of  snow  and  ice,  as  compared  with  water  or 
land  surfaces,  provides  positive  feedback  if  the  average  year-round 
temperature  decreases  and  the  extent  of  ice  and  snow  coverage  in- 
creases and  reflects  more  of  the  incoming  sunlight  back  to  space.  The 
result  is  to  lower  the  rate  of  heating  still  more,  particularly  in  the 
regions  closest  to  the  poles.  Columbia  University  scientists  observed 
from  a  study  of  satellite  photomaps  that  snow  and  icepack  cover 
were  more  extensive  and  of  longer  duration  in  the  early  1970's  than 
in  previous  years.  The  result,  they  reported,  was  to  increase  the 
Earth's  albedo,  reflect  more  sunlight  back  into  space,  and  change  the 
planet's  heat  balance.72  It  was  pointed  out  that  normally  vegetated 
ground  reflects  about  15  percent  to  20  percent  of  sunlight  and  a  calm 
ocean  reflects  5  percent  to  10  percent,  while  snow-covered  grassland 
or  pack  ice  reflects  about  80  percent. 

88  Otterman.  J.,  "Anthropogenic  Impact  on  the  Albedo  of  the  Earth,"  Climatic  Change, 
vol.  1,  Xo.  2,  1977,  pp.  137-155. 

70  "Living  With  Climatic  Change,"  proceedings  of  a  conference/workshop  held  in  Toronto, 
Not.  17-22,  1975  ;  Ottawa,  Science  Council  of  Canada,  1976,  p.  88. 

71  Hobbs,  P.  V.,  H.  Harrison,  and  E.  Robinson,  "Atmospheric  Effects  of  Pollutants,"  pp. 
910,  911. 

72  The  atmosphere  is  principally  heated  by  terrestrial  reradiation,  thus  the  reflected 
incoming  light,  escaping  back  into  space  instead  of  being  transformed  into  heat,  represents 
a  deficit  in  the  Earth's  energy  balance. 


They  also  found  that  snow  and  ice  covered  twice  as  much  ground 
in  October  1972  as  in  October  1968  and  correlated  that  situation  with 
a  drop  in  global  air  temperatures.  They  warned  that  the  potential 
for  fast  changes  of  climate  evidently  does  exist  and  should  be  kepfe 
in  mind.73 

There's  yet  another  contributor  to  the  planet's  albedo :  airborne  par- 
ticles, particularly  the  extremely  fine  dust  particles  that  have  been 
carried  too  high  in  the  atmosphere  to  be  scavenged  and  washed  out 
by  precipitation  processes.  Many  of  these  particles  remain  aloft  for 
months  or  years.  Dust  of  various  kinds  may  initiate  short-term  cool- 
ing trends  with  characteristic  time  spans  of  decades  or  centuries.  This 
depends  on  the  optical  properties  of  the  particles,  which  in  turn  de- 
pend on  particle  composition  and  size  distribution.  Furthermore,  par- 
ticles radiate  in  the  infrared,  and  therefore  can  alter  the  outgoing 
long-wave  radiation. 

Densely  populated  regions  tend  to  have  higher  albedos  than  do 
forests  or  cultivated  soils.  The  deserts  of  the  world  have  a  highei 
albedo  than,  for  example,  grass-covered  fields.  Urbanization,  agricul- 
ture, transportation  networks — all  act  to  alter  the  surface  albedo. 
While  local  changes  in  albedo  have  been  determined,  however,  the 
overall  integrated  global  variation  is  still  unknown.  Even  local  net 
effects  of  surface  changes  may  not  be  fully  understood,  since  changes 
in  the  nature  of  a  surface  are  generally  accompanied  by  change  in 
surface  roughness.  Surface  roughness  alterations  can  affect  the  man- 
ner and  rate  of  heat  and  momentum  exchanges  with  the  atmosphere 
through  modification  of  small-scale  turbulent  processes.74 

A  factor  such  as  roughness  of  the  ocean  should  not  be  overlooked 
in  ocean/atmosphere  exchange  mechanisms.  Ocean  surface  pollution 
may  also  figure  in  the  alteration  of  the  albedo  as  well  as  the  sea  surface 
characteristics:  an  oil  slick  forming  a  surface  film  on  the  sea.  for 


Beginning  in  the  1940's,  large  areas  of  the  Texas  Panhandle,  western 
Oklahoma,  Kansas,  and  Nebraska  came  under  widespread  irrigation. 
This  large-scale  irrigation  adds  more  moisture  to  the  air  through 
evaporation;  has  made  large  land  surfaces  greener  (which  changes 
the  albedo) ;  and  may  act  to  decrease  dust  in  the  air.  Since  the  situation 
is  somewhat  analogous  to  a  large-area  rain  modification  project,  a 
number  of  studies  have  been  conducted  to  ascertain  if  greater  rainfall 
could  occur  in  the  vicinity  or  downwind  of  irrigated  areas. 

Schickedanz  (1976)  provided  strong  evidence  of  irrigation-related 
anomalies;  specifically,  increased  rainfall  during  months  when  irri- 
gation took  place  in  and/or  surrounding  large  irrigated  areas  of  the 
Groat  Plains. 

The  percent  rain  increase  associated  with  the  irrigation  effect  was 
found  to  vary  from  14  percent  to  26  percent  in  June,  57  percent  to 
91  percent  in  July,  15  percent  to  26  percent  in  August,  and  19  percent 

73  Kukla,  George  .T.,  and  Helena  J.  Kukla,  "Increased  Surface  Albedo  in  the  Northern 
Hemisphere,"  Science,  vol.  183,  Feb.  22,  1974,  pp.  709,  713,  714. 

A  growing  fraction  of  current  evidence  seems  to  suggest,  however,  that  this  has  not  been 
the  in  North  America.  Analysis  of  satellite  data  for  the  last  decade  has  led  scientists 
with  the  National  Environmental  Satellite  Service  to  conclude  that  North  American  anow 
cover  showed  no  significant  change  during  the  entire  period  of  record.  Rather,  the  North 
American  total  winter  snow  cover  appears  to  be  remarkably  similar  year  to  year.  Eurasion 
snow  cover  on  the  other  hand  was  reported  to  be  much  more  variable. 

w  National  Research  Council,  Committee  on  Atmospheric  Sciences,  "Weather  and 
Climate  Modification  :  Problems  and  Progress,"  p.  156. 


]  to  35  percent  during  summer  depending  on  the  location  and  size  of 
the  irrigated  areas  in  the  States  of  Kansas,  Nebraska,  Oklahoma,  and 

Acting  similarly  to  the  manner  in  which  urban  industrial  centers 
affect  weather  in  and  downwind  of  them,  irrigated  areas  may  be  said 
to  be  a  focal  point  for  both  rain  initiation  and  rain  enhancement  or 
redistribution,  under  conditions  when  rain  is  likely.75' 76 

Stick!  (1975)  also  found  evidence  of  irrigation-related  rainfall 
,  anomalies  in  the  Columbia  Basin  of  Washington.  Explaining  that  the 
increase  in  rainfall  is  real,  he  offered  the  following  explanation : 

The  moisture  added  by  irrigation  is  evaporated  and  must  eventually  return 
I  to  the  Earth's  surface  as  precipitation.  The  question  is  where  and  when?  The 
[Columbia]  basin  is  nearly  surrounded  by  mountains.  The  surface  layer  of  air 
in  the  basin  will  eventually  be  carried  over  the  mountains  [at  the  eastern  margin 
of  the  basin],  and  if  additional  moisture  has  been  added  to  the  air  *  *  *  air,  we 
would  expect  additional  precipitation  in  the  foothills.  This  appears  to  be  what 
happens  during  the  two  months  [of  July  and  August]  when  additional  evapora- 
tion is  greatest.77 


In  review,  tables  2,  3,  and  4  summarize  much  of  the  pertinent  infor- 
mation presented  in  the  preceding  sections.  They  are,  respectively, 
"Inadvertent  Effects  on  Ten  Weather  Phenomena,"  "Chronic  Low- 
Level  Pollutants :  Mankind's  Leverage  Points  on  Climate,"  and  "Pos- 
sible Causal  Factors  in  Future  Climatic  Change  to  the  Year  2000  A.D." 



Certainty  of  inad-      Scale  of  inadvertent    cance  of  inadvert- 
Phenomenon  vertent  effect  effect  ent  effect 

1.  Visibility  and  haze  







2.  Solar  radiation  and  sunshine  




3.  Cloudiness  






4.  Precipitation  (quantity).  





 Meso  or  macro  


Precipitation  (quality)..  










5.  Thunderstorms  (hail/heavy  rain)  







6.  Severe  storms  (tornados,  other)  




7.  Temperature   





 Populated  meso  


8.  Wind/circulation.  






9.  Fog  



10.  Humidity  





i  From  "Final  Report  to  the  National  Science  Foundation  on  the  Third  Inadvertent  Weather  Modification  Workshop,'! 
Hartford,  Conn.,  May  23-27, 1977.  Hartford.  The  Center  for  Environment  and  Man,  Inc.,  1977. 

Note.— Micro:  less  than  or  equal  to  1  km;  urban:  less  than  or  equal  to  30  km;  meso:  30  to  150  km;  macro:  greater  than 
150  km. 

75  Schickedanz,  Paul  T..  The  Effect  of  Irrigation  on  Precipitation  In  the  Great  Plains. 
Final  report  on  an  investigation  of  potential  alterations  in  summer  rainfall  associated 
with  widespread  irrigation  in  the  Great  Plains,  Urbana,  111.,  Illinois  State  Water  Survey, 

1976.  105  pp. 

76  Schickendanz,  Paul  T.,  "Extra-Area  Effects  from  Inadvertent  Weather  Modification." 
In  preprints  of  Sixth  Conference  on  Planned  and  Inadvertent  Weather  Modification, 
Champaign-Urbana,  111.,  Oct.  10-13,  1977.  Boston,  American  Meteorological  Society, 

1977,  pp.  134-137. 

"Stidd,  Charles  K.,  "Irrigation  Increases  Rainfall?"  Science,  vol.  188,  Apr.  18,  1975, 
pp.  279-281.  In  Effect  of  Large-Scale  Irrigation  on  Climate  in  the  Columbia  Basin, 
Science,  vol.  184,  Apr.  12,  1974,  pp.  121-127.  Fowler  and  Helvey  argue  that  small  scale 
site  changes  may  occur,  but  the  widespread  climatic  effects  of  irrigation  may  well  be 
minimal.  Furthermore,  they  contend  that  the  available  precipitation  records  for  the 
basin  do  not  verify  Stidd's  conclusion  that  precipitation  increased  because  of  irrigation. 




Tssues  in  Inadvertent  Weather  and  Climate  Modification 
climatic  barriers  to  long-term  energy  growth 
Revelle  and  Suess  (1957)  stated: 

Human  beings  are  now  carrying  out  a  large  scale  geophysical  experiment  of 
a  kind  that  could  not  have  happened  in  the  past  nor  be  repeated  in  the  future. 
Within  a  few  centuries  we  are  returning  to  the  atmosphere  and  ocean  the  con- 
centrated organic  carbon  stored  in  the  sedimentary  rocks  over  hundreds  of  mil- 
lions of  years.  This  experiment  may  yield  a  far-reaching  insight  into  the  processes 
of  determining  weather  and  climate.78 

Thus  stated  is  the  case  for  diligent  observation  of  the  consequences 
of  the  man-generated  flux  of  carbon  dioxide  to  the  atmosphere.  Left 
unstated  is  perhaps  the  greater  need  to  anticipate  the  consequences 
well  enough  to  keep  them  within  acceptable  limits. 

Even  though  carbon  dioxide  makes  up  a  small  fraction  (less  than 
one  one-thousandth  of  the  total  atmospheric  mass)  of  the  gases  that 
comprise  the  atmosphere,  it  is  crucial  in  determining  the  Earth's 
temperature  because  it  traps  some  of  the  Earth's  heat  to  produce  the 
so-called  greenhouse  effect. 

Worldwide  industrial  civilization  may  face  a  major  decision  over 
the  next  few  decades — whether  to  continue  reliance  on  fossil  fuels  as 
principal  sources  of  energy  or  to  invest  the  research  and  engineering 
effort,  and  the  capital,  that  will  make  it  possible  to  substitute  other 
energy  sources  for  fossil  fuels  within  the  next  50  years.  The  second 
alternative  presents  many  difficulties,  but  the  possible  climatic  con- 
sequences of  reliance  on  fossil  fuels  for  another  one  or  two  centuries 
may  be  critical  enough  as  to  leave  no  other  choice. 

The  climatic  questions  center  around  the  increase  in  atmospheric 
carbon  dioxide  that  might  result  from  continuing  and  increasing  use 
of  fossil  fuels.  In  110  years  since  about  1860  a  12-percen.t  increase  in 
the  concentration  of  carbon  dioxide  had  taken  place,  but  because  of 
the  exponential  nature  of  the  consumption  of  energy  and  the  burning 
of  fossil  fuels  the  next  10-12  percent  increase  would  take  only  about 
20  years  and  the  next  10-12  percent  increase  beyond  that  only  about 
10  years.  By  this  time  the  climatic  impact  of  the  carbon  dioxide  should 
(according  to  model  calculations)  cause  a  climatic  warming  of  about 
1°C  (1.8°F).  Four  questions  are  crucial : 

1.  What  concentrations  of  carbon  dioxide  can  be  expected  in  the 
atmosphere  at  different  times  in  the  future,  for  given  rates  of  combus- 
tion of  fossil  fuels  ? 

2.  What  climatic  changes  might  result  from  increased  atmospheric 
carbon  dioxide? 

3.  What  would  be  the  consequences  of  such  climatic  changes  for 
human  societies  and  for  the  natural  environment  ? 

4.  "What,  if  any,  countervailing  human  actions  could  diminish  the 
climatic  changes  or  mitigate  their  consequences  ?  79 

Whether  such  a  warming  would  influence  the  extent  of  ice  and  snow 
at  the  polar  caps  or  influence  the  level  of  the  world  ocean  cannot  be 

■«  Rpvelle  R.  and  H.  E.  Suess,  "Carbon  Dioxide  Exchange  Between  the  Atmosphere 
and  Ocean,''  and  the  "Question  of  an  Increase  in  Atmospheric  Carbon  Dioxide  During 
the  Past  Decades,"  Tellus.  vol.  9,  No.  1,  1957,  p.  18.  .  „ 

n  National  Research  Council,  Geophysics  Research  Board,  "Energy  and  Climare,    p.  1. 


said  with  certainty.  Neither  can  it  be  said  whether  such  a  warming 
would  push  the  grain  belts  of  the  world  poleward  by  several  hundred 
kilometers  thereby  disrupting  the  present  patterns  of  agriculture. 
These  are  possibilities,  but  climatic  theory  is  yet  too  crude  to  be  certain. 
The  only  certain  proof  that  the  carbon  dioxide-greenhouse  theory  is 
correct  will  come  when  the  atmosphere  itself  ''performs  the  experi- 
ment" of  proving  present  estimates  too  high,  or  too  low.  An  important 
point  remains,  though,  and  that  is :  The  uncertainty  in  present  scien- 
tific estimates  of  potential  climatic  consequences  of  increased  energy 
use  is  not  biased  toward  optimism.80 

Carbon  dioxide  is  not  the  only  byproduct  of  the  burning  of  fossil 
fuels.  Another  form  of  atmospheric  pollution  results  from  the  intro- 
duction of  dust  and  smoke  particles,  which,  when  suspended  in  air.  are 
called  atmospheric  aerosols.  The  word  "aerosols"  is  a  term  used  to 
describe  the  suspension  of  any  kind  of  particle  in  a  gas.  These  particles 
can  be  solid  like  dust,  sand.  ice.  and  soot.  Or  they  can  be  droplets  like 
the  water  particles  in  clouds  and  fog  or  the  liquid  chemicals  that  are 
dispensed  as  droplets  from  aerosol  spray  cans.  The  air  contains  tril- 
lions upon  trillions  of  aerosol  particles,  which,  like  carbon  dioxide, 
comprise  only  a  minute  fraction  of  the  total  atmospheric  mass. 

Despite  their  relatively  small  volume,  aerosols  can  affect  the  climate, 
primarily  by  absorbing  and  scattering  back  to  space  some  of  the  sun- 
light that  could  have  otherwise  reached  the  Eartlrs  surface.  Industry 
is  not  the  only  human  activity  that  causes  aerosols.  They  are  also  pro- 
duced in  great  quantities  by  a  variety  of  agricultural  activities  and 
practices,  and  a  significant  fraction  of  the  particle  loading  of  the 
atmosphere  is  of  natural  origin. 

A  consensus  among  scientists  today  would  not  be  forthcoming  as  to 
whether  an  increase  in  aerosols  would  result  in  a  cooling  of  the  climat  <3 
or  a  warming  of  the  climate,  because  aerosols  will  cool  the  climate  if 
they  are  relatively  whiter  than  the  surface  over  which  they  lie,  or, 
alternatively,  they  will  warm  the  Earth  if  they  are  relatively  darker 
than  the  surface  over  which  they  are  suspended.  The  dust  that  exists  in 
the  atmosphere  today  is  highly  nonuniform  in  both  geographic  distri- 
bution and  relative  brightness  as  compared  to  the  underlying  surface. 
Therefore,  one  cannot  be  absolutely  certain  whether  dust  contributes 
to  climatic  warming  or  can  be  implicated  in  climatic 



Putting  together  the  different  parts  of  the  story  of  climate  and 
energy,  what  picture  emerges?  How  seriously  do  we  respond  to  the 
possibility  that  the  present  rate  of  increase  of  fossil  fuel  burning  is 
likely  to  have  noticeable  consequences  for  climate  by  the  end  of  this 
century,  but  not  become  a  serious  problem  until  well  into  the  next 
century?  On  the  longer  time  scale,  the  picture  that  emerges  is  rather 
startling  in  the  words  of  Dr.  Wallace  Broecker  of  the  Lamont-Doherty 
Geological  Observatory,  who  explains,  "Consumption  of  the  bulk  of 
the  world's  known  fossil  fuel  reserves  would  plunge  our  planet  into  a 

80  Schneider,  Stephen  H.,  "Climate  Change  and  the  World  Predicament."  Climatic 
Change,  vol.  1,  No.  1,  March  1977,  pp.  31-33. 
61  Ibid.,  pp.  34,  35. 


superinterglacial,  the  likes  of  which  the  world  lias  not  experienced  in 
the  last  million  years."  82 

Admittedly,  we  are  talking  here  of  possibilities,  not  certainties.  The 
climatic  consequences  of  massive  fossil  fuel  consumption  may  be  less 
severe  than  assessments  project,  but  they  might  be  more  severe.  Man- 
kind eventually  may  discover  a  new  energy  source  that  will  obviate  the 
need  to  use  fossil  reserves  so  extensively  for  that  purpose,  and  yet  a 
fossil-fuel-free  world  in  the  relatively  near  future  is  so  bizarre  an  idea 
it  is  hard  even  to  talk  about  it  seriously.  Or  perhaps  technology  could 
develop  a  cosmetic,  such  as  the  introduction  of  an  artificial  dust  layer 
surrounding  the  Earth  to  screen  some  of  the  incoming  sunlight.  This 
could  tend  to  offset  the  warming  effect  of  the  added  carbon  dioxide. 

What  would  happen  if  society  elected  to  ignore  the  problem  of 
carbon  dioxide  until  it  manifested  itself  (perhaps  in  another  20  years) 
in  the  form  of  a  clear  signal  that  a  global  warming  trend  had  begun 
that  was  unmistakably  attributable  to  the  further  accumulation  of 
carbon  dioxide  in  the  atmosphere?  Delaying  until  then  a  mandated 
action  to  phase  over  the  principal  energy  sources  from  fossil  fuels  to 
other  alternative  kinds  of  fuels  and  taking  into  account  another 
several  decades  for  the  transition  to  be  completed  would  put  us  half- 
way into  the  next  century  before  the  problem  could  be  shut  off  at  its 
source.  But  perhaps  the  most  disturbing  aspect  of  the  carbon  dioxide 
problem  is  that  the  effects  of  carbon  dioxide  would  endure  for  hundreds 
of  years,  even  after  the  abandonment  of  the  fossil  fuel  economy,  because 
of  the  long  recovery  time  associated  with  the  processes  that  would  rid 
the  atmosphere  of  excess  carbon  dioxide  and  establish  an  equilibrium 

This  carbon  dioxide  Sword  of  Damocles,  if  indeed  it  exists,  implies 
development  of  solar  (including  wind,  ocean,  biomass,  etc.)  fisson, 
fusion,  and  geothermal  at  a  somewhat  more  rapid  pace  than  is  gen- 
erally recognized.83 

Asserts  J.  Murray  Mitchell,  Jr. : 

The  alternative  is  clear.  Ours  is  the  generation  that  must  come  to  grips  with 
the  carbon  dixoide  problem  and  mount  a  vigorous  research  effort  to  allow  us  to 
understand  all  of  its  ramifications  for  the  future.  Ours  is  the  generation  that  may 
have  to  act,  and  act  courageously,  to  phase  out  our  accustomed  reliance  on  fossil 
fuels  before  we  have  all  the  knowledge  that  we  would  like  to  have  to  feel  that 
such  action  is  absolutely  necessary.  *  *  *  We  can  scarcely  afford  to  leave  the 
carbon  dioxide  problem  to  the  next  generation.84 


Despite  everything  that  science  has  learned  about  the  broad  charac- 
teristics of  climate  and  climatic  history,  relatively  little  is  known  of 
the  major  processes  of  climatic  change.  Lack  of  knowledge  still  is  a 

82  Mitchell,  J.  Murray^  Jr.,  "Carbon  Dioxide  and  Future  Climate,"  p.  9. 

83  Rotty,  R.  M.  and  A.  M.  Weinherg,  "How  Long  Is  Coal's  Future,"  pp.  o5-57. 
M  Mitchell,  J.  Murray,  Jr.,  "Carbon  Dioxide  and  Future  Climate,"  p.  9. 


major  barrier  to  accurate  forecasting  and  understanding  of  potential 
inadvertent  modification  of  weather  and  climate.  The  atmosphere  and 
the  ocean  make  up  such  a  complex  and  rapidly  changing  system  that 
even  short-range  forecasts  may  often  be  incorrect.  Gathering  sufficient 
information  about  global  climate  is  of  importance  if  atmospheric 
scientists  are  to  construct  the  detailed  computerized  models  capable  of 
rapidly  analyzing  enormous  amounts  of  data  concerning  each  com- 
ponent of  the  climatic  system,  which  includes  not  only  the  atmosphere 
but  the  world  ocean,  the  ice  masses,  and  the  exposed  land  surface. 

Observations  are  essential  to  the  development  of  an  understanding 
of  climatic  change.  Without  them,  theories  will  remain  theories  and 
models  would  be  of  limited  usefulness.  Observational  records  need  to 
be  extended  in  both  time  and  space  to  facilitate  adequate  documenta- 
tion of  the  climatic  events  that  have  occurred  in  the  past  and  monitor- 
ing of  the  climatically  important  physical  processes  occurring  now. 

Knowledge  of  the  mechanisms  of  climatic  change  may  be  at  least  as 
fragmentary  as  the  state  of  the  data.  Not  only  are  the  basic  scientific 
questions  largely  unanswered,  but  in  many  cases  not  even  enough  is 
known  to  pose  the  key  questions.  What  are  the  most  important  causes 
of  natural  climatic  variation,  and  which  are  the  most  important  or 
most  sensitive  of  the  many  processes  involved  in  the  interaction  of  the 
air,  sea,  ice,  and  land  components  of  the  climatic  system  ?  There  is  no 
doubt  that  the  Earth's  climates  have  changed  in  the  past  and  will  likely 
change  in  the  future.  But  will  it  be  possible  to  recognize  the  first  phases 
of  a  truly  significant  climatic  change  when  it  does  occur  ? 

In  a  1975  report,  "Understanding  Climate  Change :  A  Program  for 
Action/'  the  U.S.  Committee  for  the  Global  Atmospheric  Research 
Program  of  the  Xational  Research  Council  enumerated  the  principal 
approaches  to  these  problems  emphasizing  the  interdependence  of  the 
major  components  of  a  climatic  research  program  and  posing  a  number 
of  key  questions.  The  components  included : 

Climatic  data  analysis :  What  has  happened  in  the  past? 

Empirical  studies :  How  does  the  system  work? 

Monitoring :  What  is  going  on  now  ? 

Numerical  models:  What  is  shown  by  climatic  simulations? 

Theoretical  studies :  How  much  do  we  really  understand  ? 

Climatic  impacts :  What  does  it  all  mean  to  man  ? 

Future  climates :  How  and  when  is  the  climate  going  to  change  ? 
The  various  components  of  the  climatic  research  program  are  to  a 
great  extent  interdependent :  Data  are  needed  to  check  general  circula- 
tion models  and  to  calibrate  the  simpler  models ;  the  models  are  needed 
to  test  hypotheses  and  to  project  future  climates :  monitoring  is  needed 
to  check  the  projections ;  and  all  are  needed  to  assess  the  consequences.85 

85  National  Research  Council,  U.S.  Committee  for  the  Global  Atmospheric  Research 
Program.  "Understanding  Climatic  Change  :  A  Program  for  Action,"  Washington,  National 
Acadmy  of  Sciences,  1975,  pp.  5,  6. 



Effort  Frequency 

variable  or  index  Method  Coverage  required •  required2 

Atmospheric  indices: 

Solar  constant  Satellite  Global   N  W 

Absorbed  radiation,  albedo   do   do   P  W 

Latent  heating...  do.   N  W 

Surface  latent  heat  flux  do   World  ocean   N  W 

Surface  sensible  heat  flux  do   Regional   N  W 

Cloudiness   do   Global   P  W 

Surface  wind  over  ocean  Radar  scattering   World  ocean  N  W 

Oceanic  indices: 

Sea-surface  temperature  Ships,  satellites,  buoys...  World  ocean   E  W 

Surface-layer  heat  storage  XBT,  AXBT,  buoys  Mid-latitude   and   low-   E,  N  W 

latitude  oceans. 

Heat  transport  Moored  buoys  Selected  sections   N  W 

Temperature  structure  .Ships    do   E  S 

Surface  salinity  Ships,  buoys.   High  latitudes   E  W 

Sea  level  .1  Tide  gauges  Selected    coastal    and   E  W 

island  sites. 

Composition,  dissolved  gases  Conventional  sampling. Selected  sections  E  S 

Cryospheric  indices: 

Floating  ice  extent  Satellite   Polar  seas,  lakes  E  M 

Ice-sheet  budget  parameters   do  Greenland,  Antarctica  N  Y 

Mountain  glacier  extent  do  Selected  sites   E  Y 

Snow  cover.  do   Continents   E  M 

Surface  and  hydrologic  indices: 

River  discharge    Flow  gauges  Selected  sites  E,  N  W 

Soil  moisture  Satellite  Land  areas  E  W 

Lake  levels  Gauges   Selected  sites   E  W 

Precipitation  Satellite,  radar,  gauges...  Global   E  W 

Composition  and  turbidity  indices: 

Chemical  composition  Sampling  Selected  sites   E  S 

Aerosols  and  dust  Satellite  Global.   E  W 

Anthropogenic  indices: 

Thermal  pollution  Sampling..  Continents  and  coasts  N  W 

Air  and  water  pollution  do  Global..   E  W 

Land  use  Satellite  Continents  E  Y 

1  N,  completely  new  monitoring  effort  required;  E,  expansion  of  present  monitoring  efforts  required;  P,  present  (or 
slightly  expanded)  monitoring  efforts  satisfactory  but  coordination  and  further  analysis  required, 
a  W,  weekly  (or  possibly  daily  in  some  cases);  M,  monthly;  S,  seasonally;  Y,  yearly  (or  possibly  decadal  in  some  cases). 

Source:  Natichal  Research  Council,  U.S.  Committee  for  the  Global  Atmospheric  Research  Program,  "Understanding 
Climatic  Change:  A  Program  for  Action,"  Washington,  National  Academy  of  Sciences,  1975;  pp.  78-79. 

The  Committee  on  Atmospheric  Sciences,  also  of  the  National  Re- 
search Council,  stated  in  a  1973  report  entitled  "Weather  and  Climate 
Modification :  Problems  and  Progress"  that  if  society  is  to  deal  with 
long-term  problems  of  inadvertent  weather  modification  and  climatic 
changes  caused  by  man  and  his  activities,  then  urgent  attention  and 
action  are  required  at  the  earliest  possible  moment.  The  Committee 
outlined  several  courses  of  action  that  should  be  undertaken,  each  con- 
tributing to  a  part  of  the  necessary  work  to  be  accomplished: 

1.  A  worldwide  network  of  ground-based  stations  is  needed  to  moni- 
tor the  properties  of  the  atmosphere  with  particular  attention  being 
given  to  those  gases  and  aerosols  affecting  radiation  and  heat  transfer. 
Precipitation  collection  should  be  undertaken  for  the  analysis  of 
atmospheric  chemical  constituents.  Surface  monitoring  efforts  should 
also  be  augmented  by  airborne  monitoring  of  particles  and  gases  in  the 
atmosphere.  Table  5  summarizes  in  detail  the  variables  to  be  moni- 
tored, the  method  of  monitoring,  coverage,  effort  required  and  fre- 
quency required. 

2.  Since  influence  on  climate  caused  by  human  factors  is  a  global 
matter,  internationally  cooperative  plans  should  be  established  that 
will  provide  long-term  and  uniform  monitoring  data. 


3.  Continuous  monitoring  of  the  Earth  by  satellites  should  be  devel- 
oped to  measure  not  only  cloud  cover  and  cloud  types  but  also  the  ther- 
mal characteristics  of  the  atmosphere  and  the  Earth's  surface,  as  well 
as  related  variations  in  the  albedo  of  the  Earth.  Satellite  measurements 
should  be  complemented  by  a  program  of  ground-based  remote  sensing 
of  the  dynamical,  chemical,  and  particulate  properties  of  the 

4.  Computer  capabilities  for  simulation  of  climate  and  climatic 
changes  should  be  fully  utilized.  Climatic  models  eventually  may  prove 
to  be  quite  different  from  the  present  general  circulation  models.  How- 
ever, if  we  are  to  reach  the  capability  to  assess  the  consequences  of 
further  human  intervention,  climatic  model  development  must  be 
promptly  undertaken.86 

Many  of  the  efforts  envisaged  are  of  an  obvious  international  charac- 
ter, and  the  degree  to  which  they  should  be  regarded  as  national  versus 
international  activities  is  not  of  critical  importance.  The  important 
point  is,  however,  that  there  are  international  efforts  now  underway  of 
drect  relevance  to  the  climatic  problem. 

The  World  Meteorological  Organization  (WMO)  and  the  Interna- 
tional Council  of  Scientific  Unions  (ICSU)  jointly  organized  a  global 
atmospheric  research  program  (GARP)  in  1967.  GARP  goals  in- 
clude :  providing  the  improved  understanding  of  the  global  circulation 
needed  to  extend  the  range  and  accuracy  of  weather  forecasts;  under- 
standing the  physical  basis  of  climate  and  climatic  fluctuations ;  and 
providing  a  firm  foundation  for  the  World  Weather  Watch 

Several  GARP  regional  expirements  are  planned  in  order  to  exam- 
ine specific  processes.  Hie  GARP  Atlantic  Tropical  Experiment 
(GATE)  followed  the  Barbados  Oceanographic  and  Meteorological 
Experiment  (BOMEX,  1969)  in  a  succession  of  experiments  designed 
to  gain  increased  understanding  of  the  atmosphere  and  the  causes  of 
climatic  variation  and  change.  The  primary  objective  of  GATE  was 
to  learn  more  about  the  meteorology  of  the  tropical  equatorial  belt 
where  vast  quantities  of  heat  and  moisture,  carried  upward  by  orga- 
nized convective  systems,  are  transported  and  redistributed  to  higher 
latitudes,  ultimately  affecting  global  atmospheric  circulation  patterns. 
Because  the  tropics  are  believed  to  be  a  key  to  these  circulation  pat- 
terns, scientists  expect  data  from  GATE  to  help  them  better  under- 
stand the  global  climate  machine.  Conducted  as  scheduled  from  June  15 
to  September  30,  1974,  GATE  had  the  cooperation  of  some  72  coun- 
tries. In  addition  to  BOMEX  and  GATE,  experiments  designed  to 
contribute  to  the  understanding  of  specific  oceanic-atmospheric  proc- 
esses in  selected  regions  are  :  the  Air  Mass  Transformation  Experiment 
( AMTEX) ,  the  Monsoon  Experiment  (MONEX) ,  and  the  Polar  Ex- 
periment (POLEX).  These  regional  experiments  and  the  knowledge 
gleaned  from  them  will  culminate  in  a  truly  international  global  ob- 
serving experiment,  the  First  GARP  Global  Experiment  (FGGE) 
scheduled  for  the  late  1978-79  timeframe. 

86  National  Research  Council.  Committee  on  Atmospheric  Sciences,  'Weather  and  Climate 
Modification  :  Problems  and  Progress,"  pp.  160,  161. 

87  WWW  is  an  operational  program  of  member  nations  of  the  WMO  for  making  available 
the  basic  meteorological  and  related  environmental  information  needed  by  each  member 
aation  to  supplement  and  support  Its  meteorological  services  and  research. 

34-857—79  15 


The  program  goals  of  GARP  intersect  with  the  objectives  of  other 
international  environmental  programs.  One  such  program  is  the  Inter- 
governmental Oceanographic  Commission  Integrated  Global  Ocean 
Station  System  (IGOSS)  being  developed  jointly  with  the  World 
Meteorological  Organization  to  provide  more  extensive  and  timely 
information  for  analysis  and  prediction  of  the  state  of  the  oceans  and 
for  research  purposes.  This  is  accomplished  through  the  development 
of  a  comprehensive  monitoring  system  for  the  total  physical  ocean- 
atmosphere  environment.  Another  is  EARTH  WATCH,  a  major  com- 
ponent of  the  United  Nations  Enviornment  Program  (UNEP)  being 
developed  to  monitor  and  assess  the  state  of  the  oceans,  atmosphere, 
land  and  human  health  in  order  that  rational  decisions  can  be  made 
for  the  management  of  the  environment.  EARTHWATCH  will  also 
interact  with  and  depend  on  the  monitoring  and  research  capabilities 
of  GARP.  A  key  component  of  the  UNEP/EARTHWATCH  global 
baseline  and  regional  monitoring  effort  is  the  Global  Environment 
Monitoring  System,  which  is  designed  to  measure  and  monitor 
priority  pollutants  and  related  factors  of  the  atmospheric  environ- 
ment, thus  permitting  quantitative  assessment  of  the  global  impact 
of  manmade  and  natural  influences  on  weather  and  climate. 

The  Global  Observing  System  provides  worldwide  meteorological 
and  related  environment  observation  data  needed  by  the  World 
Weather  Watch  and  GARP.  The  overall  system  consists  of  two  subsys- 
tem? :  a  space-based  satellite  subsystem,  composed  of  two  types  of 
satellites,  those  in  polar  orbit  and  those  in  geostationary  orbit;  and  a 
surf  ace-based  subsystem  composed  of  basic  synoptic  surface  and  upper 
air  networks,  other  networks  of  stations  on  land  and  sea,  and  aircraft 
meteorological  observations. 

The  U.S.  Committee  for  the  Global  Atmospheric  Research  Program 
believes  that  these  observational  programs  planned  in  support  of 
GARP  offer  an  unparalleled  opportunity  to  observe  the  global  atmos- 
phere, and  furthermore  that  every  effort  should  be  made  to  use  these 
data  for  climatic  purposes  as  well  as  for  the  purposes  of  weather  pre- 
diction. The  Committee  emphasized  however,  that  the  climatic  system 
consists  of  important  nonatmospheric  components,  including  the 
world's  oceans,  ice  masses,  and  land  surfaces,  together  with  elements 
of  the  biosphere.  While  it  is  not  necessary  to  measure  all  of  these  com- 
ponents in  the  same  detail  with  which  the  atmosphere  is  observed, 
their  roles  in  climatic  variation  should  not  be  overlooked.88 

The  Committee's  1975  report,  "Understanding  Climatic  Change: 
A  Program  for  Action,"  further  stated  that : 

The  problem  of  climatic  variation  differs  from  that  of  weather  forecasting  by 
the  nature  of  the  data  sets  required.  The  primary  data  needs  of  weather  predic- 
tion are  accurate  and  dense  synoptic  observations  of  the  atmosphere's  present 
and  future  states,  while  the  data  needed  for  studies  of  climatic  variation  are 
longer-term  statistics  of  a  much  wider  variety  of  variables.  When  climatic  varia- 
tions over  long  time  scales  are  considered,  these  variables  must  be  supplied  from 
fields  outside  of  observational  meteorology.  Thus,  an  essential  characteristic  of 
climate  is  its  involvement  of  a  wide  range  of  nonatmospheric  scientific  disciplines, 
for  example,  oceanography,  glaciology,  hydrology,  astronomy,  geology,  and 
paleantology  as  well  as  from  the  biological  and  social  sciences  of  ecology,  geog- 
raphy,  archaeology,  history,  economics,  and  sociology. 

88  N'.-itionnl  Research  Council,  U.S.  Committee  for  the  Global  Atmospheric  Research 
Program,  "Understanding  Climatic  Change:  A  Program  for  Action,"  pp.  105,  106. 


The  types  of  numerical  models  needed  for  climatic  research  also  differ  from 
those  of  weather  prediction.  The  atmospheric  general  circulation  models  do  not 
need  a  time-dependent  ocean  for  weather-forecasting  purposes  over  periods  of  a 
week  or  two.  For  climatic  change  purposes,  on  the  other  hand,  such  numerical 
models  must  include  the  changes  of  oceanic  heat  storage.  Such  a  slowly  varying 
feature  may  be  regarded  as  a  boundary  or  external  condition  for  weather  predic- 
tion but  becomes  an  internal  part  of  the  system  for  climatic  variation.89 

In  view  of  these  characteristics,  the  Committee  suggested  that  while 
the  GARP  concern  with  climate  was  a  natural  one,  the  problem  of 
climate  goes  much  beyond  the  present  basis  and  emphasis  of  GARP. 
Accordingly,  they  recommended  that  the  global  climate  studies  that 
are  under  way  within  GARP  be  viewed  as  leading  to  the  organization 
of  a  new  and  long-term  international  program  devoted  specifically  to 
the  study  of  climate  and  climatic  variation,  an  international  climatic 
research  program  (ICRP). 

As  viewed  by  the  Committee  the  main  thrust  of  the  international 
climatic  program  would  be  the  collection  and  analysis  of  climatic  data 
during  a  series  of  international  climatic  decades  (ICD)  designated  for 
the  period  19S0-2000.  During  this  period,  the  cooperation  of  all  nations 
would  be  sought  to  participate  in  an  intensive  effort  to  develop  and 
secure  as  complete  a  global  climatic  data  base  as  possible.  The  Com- 
mittee urged  the  creation  of  an  international  cooperative  program  for 
the  monitoring  of  selected  climatic  indices  and  the  extraction  of  his- 
torical and  proxy  climatic  data  unique  to  each  nation,  which  would 
include,  but  not  be  limited  to,  such  indices  as  glaciers,  rain  forest  pre- 
cipitation, lake  levels,  local  desert  history,  tree  rings,  and  soil  records. 
This  would  take  the  form  of  an  international  paleoclimatic  data  net- 
work (IPDX) ,  as  a  subprogram  of  the  ICRP. 

To  promote  wider  international  participation  in  climatic  research, 
it  was  recommended  that  programs  and  activities  be  developed  to 
encourage  international  cooperation  in  climatic  research  and  to  facili- 
tate the  participation  of  developing  nations  that  do  not  yet  have  ade- 
quate training  or  research  facilities.  Internationally  supported  re- 
gional climatic  studies  describing  and  modeling  local  climatic  anom- 
alies of  special  interest  were  also  recommended.90 

The  Committee  stressed  the  importance  of  international  cooperative 
programs  to  assess  the  impacts  of  presently  observed  climatic  changes 
on  the  economies  of  the  world's  nations,  including  the  effects  on  water 
supply,  food  production,  and  energy  utilization,  as  well  as  analyses  of 
the  regional  impacts  of  possible  future  climates. 

IMd.,  p.  106. 

00  The  World  Meteorological  Organization  headquarters  in  Geneva  is  planning  a  world 
conference  on  climate,  tentatively  to  be  held  in  1979. 



(By  Robert  E.  Morrison,  Specialist  in  Earth  Sciences,  Science  Policy  Research 
Division,  Congressional  Research  Service) 

Overview  of  Federal  Activities 

The  Federal  Government  has  been  involved  for  over  30  years  in  a 
number  of  aspects  of  weather  modification,  through  activities  of  both 
the  Congress  and  the  executive  branch.  Since  1947,  weather  modifica- 
tion bills  pertaining  to  research  support,  operations,  policy  studies, 
regulations,  liabilities,  activity  reporting,  establishment  of  panels  and 
committees,  and  international  concerns  have  been  introduced  in  the 
Congress.  There  have  been  hearings  on  many  of  these  proposed  meas- 
ures, and  oversight  hearings  have  also  been  conducted  on  pertinent 
ongoing  programs.  A  total  of  six  public  laws  specifically  on  weather 
modification  have  been  enacted  since  1953,  while  others  have  included 
provisions  which  in  some  way  are  relevant  to  weather  modification. 
Resolutions  dealing  with  the  use  of  weather  modification  technology 
as  a  weapon  by  U.S.  military  forces  and  promotion  of  a  U.N.  treaty 
prohibiting  such  activities  have  been  introduced  in  both  houses  of  the 
Congress,  and  one  such  resolution  was  passed  by  the  Senate. 

Federal  legislation  has  dealt  principally  with  three  aspects  of 
weather  modification — research  program  authorization  and  direction, 
collection  and  reporting  of  weather  modification  activities,  and  the 
commissioning  of  major  studies  on  recommended  Federal  policy  and 
the  status  of  technology.  In  addition  to  providing  direction  through 
authorizing  legislation,  the  Congress  has  initiated  one  major  Federal 
program  through  an  appropriations  bill  write-in,  and  this  program 
has  since  regularly  received  support  through  additional  appropria- 
tions beyond  its  recommended  OMB  funding  level. 

Identifiable  Federal  research  and  operational  weather  modification 
programs  can  be  traced  from  at  least  the  period  of  World  War  II; 
however,  the  research  programs  of  most  agencies  other  than  the  De- 
fense Department  were  not  begun  until  the  1950's  and  1960's.  "While 
these  research  and  development  programs  sponsored  at  various  times 
by  at  least  eight  departments  and  independent  agencies  have  consti- 
tuted its  major  involvement,  the  executive  branch  has  also  performed 
a  wide  range  of  other  weather  modification  activities.  Such  activities 
include  the  conduct  of  modest  operational  programs,  coordination  of 
Federal  research  programs,  collection  and  dissemination  of  U.S. 
weather  modification  activities,  sponsoring  of  in-depth  studies,  publi- 
cation of  a  large  variety  of  reports,  negotiation  for  international  re- 
strictions barring  hostile  use  of  weather  modification,  and  cooperation 
with  other  nations  in  planning  of  international  research  projects  or 
assisting  in  foreign  operational  programs.  The  latter  two  activities, 



both  essentially  international  in  scope,  are  only  noted  here  but  are  dis- 
cussed more  fully  in  the  chapter  on  international  aspects.1 

While  some  of  the  numerous  studies  on  weather  modification  have 
been  undertaken  at  the  direction  of  the  Congress,  others  have  been 
initiated  by  one  or  more  Federal  agencies  or  by  interagency  committees 
of  the  executive  branch.  Published  reports  have  included  those  which 
present  the  findings  and  recommendations  of  the  special  studies  under- 
taken, those  which  are  published  periodically  by  agencies  or  commit- 
tees with  regular  responsibilities  for  reporting  on  Federal  programs 
or  on  operational  activities,  and  the  many  publications  on  specific  re- 
search projects  which  are  prepared  by  the  individual  agencies  or  by 
contractors  and  grantees  participating  in  the  respective  projects.  Later 
in  this  chapter  some  of  the  Federal  reports  which  fall  into  the  first  two 
categories  are  identified  under  the  discussions  of  major  studies,  Fed- 
eral structure,  and  coordination  of  weather  modification;  reports 
from  the  third  category  are  referenced  from  time  to  time  throughout 
the  report.  Some  of  the  Federal  reports  are  included  in  the  selected 
bibliography  in  appendix  H  and  many  are  also  listed  in  the  other 
major  bibliographies  which  are  referenced  in  that  appendix. 

Legislative  and  Congressional  Activities 
federal  legislation  on  weather  modification 


Congressional  interest  in  weather  modification  has  been  demon- 
strated by  the  fact  that  legislation  on  the  subject  has  been  introduced 
in  nearly  every  session  of  Congress  since  1947.  Nevertheless,  in  spite  of 
the  apparent  interest,  a  total  of  six  public  laws  relating  specifically  and 
directly  to  weather  modification  have  been  enacted  during  this  period, 
and  two  of  those  passed  were  mere  time  extensions  of  specific  provisions 
in  earlier  laws.2  Briefly,  these  laws  are : 

Public  Law  83-256  (67  Stat.  559)  of  August  13,  1953,  to  create 
an  Advisory  Committee  on  Weather  Control,  to  perform  a  com- 
plete study  and  evaluation  of  public  and  private  experiments  in 
weather  modification  to  determine  the  U.S.  role  in  research,  opera- 
tions, and  regulation ; 

Public  Law  84-664  (70  Stat.  509)  of  July  9,  1956,  to  extend  the 
authorized  life  of  the  Advisory  Committee  for  2  years  through 
June  30, 1958 ; 

Public  Law  85-510  (72  Stat.  353)  of  July  12, 1958,  to  authorize 
and  direct  the  National  Science  Foundation  to  initiate  a  program 
of  study,  research,  and  evaluation  in  the  field  of  weather  modifica- 
tion and  to  prepare  an  annual  report  to  the  Congress  and  the 
President  on  weather  modification ; 

Public  Law  92-205  (85  Stat.  736)  of  December  18, 1971,  to  pro- 
vide for  the  reporting  of  weather  modification  activities  to  the 
Federal  Government  through  the  Secretary  of  Commerce  and  for 
dissemination  of  that  information  by  the  Secretary  of  Commerce 
from  time  to  time ; 

1  See  ch.  10. 

*  Tliese  six  public  laws  are  reproduced  In  app.  I. 


Public  Law  93-436  (88  Stat.  1212)  of  October  5, 1974,  to  extend 
appropriation  authorization  for  reporting  and  disseminating 
weather  modification  activities  through  the  Secretary  of  Com- 
merce, as  prescribed  by  Public  Law  92-205,  through  1977; 

Public  Law  94-490  (90  Stat.  2359)  of  October  13,  1976,  to 
authorize  and  direct  the  Secretary  of  Commerce  to  develop  a  na- 
tional policy  on  weather  modification  and  to  extend  appropriation 
authorization  for  reporting  and  disseminating  weather  modifica- 
tion activities,  as  prescribed  by  Public  Law  92-205,  through  1930. 
Although  not  exclusively  concerned  with  weather  modification, 
another  act,  Public  Law  90^t07  of  July  18, 1968,  amended  the  National 
Science  Foundation  Act  of  1950.  Section  11  of  this  new  act  specifically 
repealed  Public  Law  85-510,  by  which  the  XSF  had  been  directed  to 
initiate  and  support  a  program  of  study,  research,  and  evaluation  in 
weather  modification  and  to  report  annually  on  the  subject. 

Another  law  of  some  significance  to  weather  modification,  though 
much  broader  in  its  overall  purpose,  was  the  fiscal  year  1962  public 
works  appropriation,  Public  Law  87-330  (75  Stat.  722)  of  Septem- 
ber 30,  1961.  Through  a  $100,000  write-in  to  this  bill,  the  Congress 
initiated  the  atmospheric  water  resources  program  (Project  Sky- 
water)  ,  conducted  by  the  Bureau  of  Reclamation  in  the  Department 
of  the  Interior.  Through  subsequent  public  works  appropriations  the 
Congress  has  continued  to  provide  direction  to  this  program  almost 
every  year  since  its  inception  and  has  provided  frequent  funding 
increases  over  levels  budgeted  by  the  administration. 

\The  Advisory  Committee  on  Weather  Control 

Between  1951  and  1953  it  was  disclosed  in  congressional  hearings  on 
several  bills  introduced  by  both  parties  that  water  users  (farmers, 
ranchers,  electric  utilities,  and  municipalities)  were  spending  between 
$3  million  and  $5  million  annually  on  weather  modification  and  that 
such  activities  covered  about  10  percent  of  the  country's  land  area.3  It 
was  the  opinion  of  the  Congress  in  1953  that  "research  and  development 
in  the  field  of  weather  modification  have  attained  the  stage  at  which  the 
application  of  scientific  advances  in  this  field  appears  to  be  practical.*' 
but  also  that  "the  effect  of  the  use  of  measures  for  the  control  of  weather 
phenomena  upon  the  social,  economic,  and  political  structures  *  *  * 
and  upon  national  security  cannot  now  be  determined.  It  is  a  field  in 
which  unknown  factors  are  involved.  It  is  reasonable  to  anticipate, 
however,  that  modification  and  control  of  weather,  if  effective  on  a 
large  scale,  would  result  in  vast  and  far-reaching  benefits  to  agricul- 
ture, industry,  commerce,  and  the  general  welfare  and  common 
defense."  4 

Recognizing  possible  deleterious  consequences  which  might  follow 
application  of  weather  modification  techniques  with  inadequate  safe- 
guards or  incomplete  understanding,  and  realizing  that  weather  modi- 
fication experiments  or  operations  could  possibly  affect  areas  extending 
across  State  and  national  boundaries,  the  Congress  considered  that  such 
activities  "are  matters  of  national  and  international  concern"  and  ac- 
cordingly, declared  it  "to  be  the  policy  of  the  Congress,  in  order  to  effect 
the  maximum  benefit  which  may  result  from  experiments  and  opera- 

a  Advisory  Committee  on  Weather  Control,  final  report,  Washington,  D.C.,  U.S.  Govern- 
ment Printing  Oflice.  Dec.  31,  1957,  vol.  I,  p.  8. 

4  Public  Law  S3-256  (67  Stat.  559),  Aug.  13,  1953,  statement  of  purpose  and  policy. 


tions  designed  to  modify  and  control  weather,  to  correlate  and  evaluate 
the  information  derived  from  such  activity  and  to  cooperate  with  the 
several  States  and  the  duly  authorized  officials  thereof  with  respect  to 
such  activity,  all  to  the  end  of  encouraging  intelligent  experimentation 
and  the  beneficial  development  of  weather  modification  and  control, 
preventing  its  harmful  and  indiscriminate  exercise,  and  fostering 
sound  economic  conditions  in  the  public  interest."  5 

In  order  to  determine  the  extent  to  which  the  United  States  should  be 
involved  in  weather  modification  research  and/or  operations  and  in  the 
regulation  of  such  activities,  the  Advisory  Committee  on  Weather  Con- 
trol was  established  by  Public  Law  83-256,  approved  August  13, 1953, 
and  was  directed  by  that  law  to  make  a  complete  study  and  evaluation 
of  public  and  private  experiments  in  weather  control. 

The  Committee  was  to  be  composed  of  Government  and  non-Govern- 
ment members  in  about  equal  number  and,  in  carrying  out  its  man- 
date, was  given  authority  to  conduct  hearings,  to  acquire  pertinent 
information  and  records  from  departments  and  agencies  of  the  execu- 
tive branch,  and  to  enlist  the  services  of  personnel  of  any  agency  of 
the  Federal  Government  (with  the  consent  of  the  agency  concerned).6 
The  Committee  was  requested  to  submit  from  time  to  time  reports  on 
its  findings  and  recommendations  to  the  President  for  submission  to 
the  Congress  and  was  directed  to  submit  its  final  report  to  the  Presi- 
dent for  transmittal  to  the  Congress  by  June  30, 1956. 7  It  became  clear 
that  the  study  was  of  such  magnitude  that  additional  time  would  be 
required  for  its  successful  completion,  and  the  Committee  requested 
that  its  life  be  extended  2  years,  noting  that  .  .  it  has  succeeded  in 
establishing  some  positive  and  important  results  which  justify  the 
Federal  Government  continuing  its  special  interest  in  the  field. " 8 
Thereupon,  the  Congress  passed  Public  Law  84-664  (70  Stat.  509) 
of  July  9,  1956,  which  extended  the  date  for  completion  of  the  report 
until  June  30,  1958.  The  final  report  of  the  Committee  was  submitted 
to  the  President  on  December  31, 1957.9 

Direction  to  the  National  Science  Foundation 

The  Advisory  Committee  on  Weather  Control  recognized  that  the 
development  of  weather  modification  rested  on  fundamental  knowl- 
edge obtainable  only  through  scientific  research  into  processes  in  the 
atmosphere  and  recommended  that  an  agency,  preferably  the  Na- 
tional Science  Foundation  (XSF),  be  designated  to  promote  and  sup- 
port meteorological  research  in  needed  fields,  to  coordinate  research 
projects,  and  to  constitute  a  central  point  for  assembly,  evaluation, 
and  dissemination  of  information.10  Accordingly,  when  the  Congress 
enacted  Public  Law  85-510  of  July  10,  1958,  which  amended  the  Na- 
tional Science  Foundation  Act  of  1950,  additional  responsibilities 
were  incorporated,  directing  the  Foundation : 

To  initiate  and  support  a  program  of  study,  research,  and  evaluation  in  the 
field  of  weather  modification,  giving  particular  attention  to  areas  that  have 

c  Ibid. 

•  Ibid.,  sec.  9. 

7  Ibid.,  sec.  10.  „   tl  y,.  _. 

s  Advisory  Committee  on  Weather  Control,  first  interim  report,  Washington.  D.C.,  Feb- 
ruary 1956,  p.  ii.  _ 

9  Advisory  Committee  on  Weather  Control.  "Final  Report  of  the  U.S.  Advisory  Com- 
mittee on  Weather  Control,"  Washington,  DC,  U.S.  Government  Printing  Office,  March  6, 
1958,  in  two  volumes.  32  and  422.  pp.  (Recommendations  of  the  Committee  are  found  in 
tbi<  chapter,  p.  2''.R.  and  in  chapter  G. ) 

:o  Ibid.,  vol.  I,  pp.  vii-vili. 


experienced  floods,  drought,  hail,  lightning,  fog,  tornadoes,  hurricanes,  or  other 
weather  phenomena,  and  to  report  annually  to  the  President  and  the  Congress 

The  In  SF  was  further  directed  to  ".  .  .  consult  with  meterologists 
and  scientists  in  private  life  and  with  agencies  of  Government  inter- 
ested in,  or  affected  by,  experimental  research  in  the  field  of  weather 
control." 12  Authority  was  given  to  NSF  to  hold  hearings,  to  require 
the  keeping  of  records  and  furnishing  of  information  on  weather 
modification  research  and  operations,  and  to  inspect  records  and 
premises  as  appropriate  in  order  to  carry  out  the  responsibilities 

In  effect,  the  NSF  was  asigned  the  "lead  agency"  role  (a  term 
which  was  in  later  years  to  become  the  subject  of  much  debate  and 
discussion)  among  Federal  agencies  involved  in  weather  modification. 
A  decade  later,  the  Foundation  was  stripped  of  these  specific  respon- 
sibilities and  of  this  lead  agency  role  when  the  Congress  again 
amended  the  National  Science  Foundation  Act  of  1950,  by  passing 
Public  Law  90-407  of  July  18, 1968.  Section  11  of  the  1968  law  struck 
section  14  and  paragraph  (9),  subsection  (a),  of  section  3  from  the 
National  Science  Foundation  Act,  terminating  as  of  September  1, 1968, 
the  responsibilities  spelled  out  in  these  sections  a  decade  earlier  with 
regard  to  weather  modification. 

The  Senate  report  which  accompanied  the  bill  subsequently  enacted 
as  Public  Law  90-407  stated  that  the  NSF  was  divested  of  these  func- 
tions ". . .  for  a  number  of  reasons :"  13 

One  [reason]  is  that  the  ramifications  of  weather  modification  are  so  broad 
as  to  encompass  far  more  issues  than  scientific  ones.  Another  is  that  progress 
in  this  area  has  reached  the  point  where  it  requires  much  developmental  work 
as  well  as  continued  research.  The  Departments  of  Commerce  and  Interior  are 
assuming  much  of  the  responsibility  in  this  area,  which  the  Foundation  may  con- 
tinue to  back  up  with  appropriate  support  for  some  of  the  research  still  needed. 
NSF  retains  ample  authority  to  continue  support  for  the  latter  .  .  .  and  clearly 
should  do  so.  The  Foundation  will  in  any  case  continue  those  research  activities 
necessary  to  preserve  continuity  in  the  program,  pending  passage  of  the  weather 
modification  legislation  now  pending.  In  the  latter  regard,  the  committee  calls 
attention  to  the  necessity  for  legislation  to  continue  elsewhere  in  the  executive 
branch  the  development  and  reporting  activities  which  NSF  will  not  have  author- 
ity to  support  after  September  1, 1968. 

Although  legislation  was  introduced  and  considered  by  the  Congress 
which  would  have  reassigned  this  lead  agency  role  to  another  agency, 
no  further  congressional  action  was  taken  on  weather  modification 
until  1971. 

Reporting  of  weather  modification  activities  to  the  Federal  Govern- 

Responsibility  for  maintaining  a  depository  for  information  on  U.S. 
weather  modification  activities  and  for  reporting  annually  on  Federal 
programs  and  the  general  status  of  the  field  rested  with  the  National 
Science  Foundation  for  the  10-year  period  from  1958  through  1968, 
after  which,  as  has  been  noted,  these  and  other  functions  were  sus- 
pended by  Public  Law  90-407. 

11  National  Science  Foundation  Act  of  1950.  as  amended  by  Public  Law  S5-510  (72  Stat' 
358)  of  July  11.  1958.  sec.  3.  subsec.  fa),  par.  (9). 

12  Ibid.,  sec.  14. 

13  U.S.  Congress.  Senate.  Committee  on  Labor  and  Public  Welfare,  "National  Science 
Foundation — Functions — Administration."  report  to  accompany  H.R.  5404.  Washington, 
U.S.  Government  Printing  Office,  1968.  (90th  CoDg.,  2d  sess.  Senate  Kept.  No.  1137.) 


After  a  lapse  of  over  3  years,  the  Congress  passed  Public  Law  92- 
205  (85  Stat.  736)  of  December  18,  1971,  which  directed  that  ".  .  .  no 
person  may  engage  or  attempt  to  engage  in  any  weather  modification 
activity  in  the  United  States  unless  he  submits  to  the  Secretary  of 
Commerce  such  reports  with  respect  thereto,  in  such  form  and  con- 
taining such  information,  as  the  Secretary  may  by  rule  prescribe.  The 
Secretary  may  require  that  such  reports  be  submitted  to  him  before, 
during,  and  after  such  activity  or  attempt."  14  The  act  further  states 
that  the  Secretary  of  Commerce  is  charged  with  responsibility  to 
maintain  a  record  of  such  weather  modification  activities  in  the  United 
States  and  to  publish  summaries  of  the  activities  "from  time  to  time" 
as  deemed  appropriate,  Such  information  received  under  the  provi- 
sions of  this  law,  with  certain  exceptions,  is  to  be  made  fully  available 
to  the  public.15  Authority  was  provided  to  the  Secretary  to  obtain  the 
required  information  by  rule,  subpena,  or  other  means  and  to  inspect 
the  records  and  premises  of  persons  conducting  weather  modification 
projects,  as  necessary,  to  carry  out  assigned  responsibilities.  There  is 
also  provision  for  levying  fines  up  to  $10,000  on  any  person  for  non- 
compliance with  the  stipulations  of  the  law  requiring  the  reporting  of 
weather  modification  activities.  Public  Law  92-205  is  concerned  with 
the  reporting  of  weather  modification  projects,  however,  not  with 
their  regulation,  control,  or  evaluation. 

Within  the  Commerce  Department,  the  weather  modification  report- 
ing system  required  by  Public  Law  92-205  is  administered  on  behalf 
of  the  Secretary  by  the  National  Oceanic  and  Atmospheric  Adminis- 
tration (NOAA).  Upon  subsequent  advertisement  of  Commerce  De- 
partment rules  in  the  Federal  Eegister,  the  requirement  for  submitting 
information  on  weather  modification  projects  became  effective  on 
November  1,  1972.  Federal  agencies  were  excluded  from  the  require- 
ment to  submit  such  information  under  the  act;  however,  upon  mutual 
agreement  by  the  agencies  to  do  so,  data  on  Federal  projects  have  also 
been  collected  and  disseminated  by  NO  A  A  as  of  November  1, 1973. 

Appropriations  for  administering  the  provisions  of  Public  Law 
92-205  were  authorized  through  June  30,  1974,  by  the  original  law. 
Additional  authorizations  for  appropriations,  extending  the  responsi- 
bility of  the  Secretary  of  Commerce  for  reporting  procedures,  were 
approved  by  the  Congress  in  two  subsequent  laws.  Public  Law  93-436 
(88  Stat.  1212)  of  October  5,  1974,  extended  reporting  requirements 
through  June  30,  1977;  while  Public  Law  94-490  (90  Stat.  2359)  of 
October  13,  1976,  contained  among  other  provisions  a  similar  exten- 
sion of  these  provisions  through  June  30, 1980.  The  major  thrust  of  the 
latter  act,  known  as  the  National  Weather  Modification  Policy  Act  of 
1976.  is  discussed  in  the  next  section. 

The  National  Weather  Modification  Policy  Act  of  1976 

After  consideration  of  a  number  of  bills  introduced  in  the  94th 
Congress  and  extensive  hearings  on  weather  modification,  the  Con- 
gress passed  Public  Law  94-490  (90  Stat.  2359)  ,  the  National  Weather 
Modification  Policy  Act  of  1976,  which  was  signed  October  13,  1976. 
The  following  particular  findings  prompted  the  Congress  to  take 
action : 

1.  weather-related  disasters  and  hazards,  including  drought, 
hurricanes,  tornadoes,  hail,  lightning,  fog,  floods,  and  frost,  result 

54  Public  Law  92-205  (85  Stat.  73G).  sec.  2. 
«  Ibid.,  sec.  3 


in  substantial  human  suffering  and  loss  of  life,  billions  of  dollars 
of  annual  economic  losses  to  owners  of  crops  and  other  property, 
and  substantial  loss  to  the  U.S.  Treasury ; 

2.  weather  modification  technology  has  significant  potential  for 
preventing,  diverting,  moderating,  or  ameliorating  the  adverse 
effects  of  such  disasters  and  hazards  and  enhancing  crop  produc- 
tion and  the  availability  of  water; 

3.  the  interstate  nature  of  climatic  and  related  phenomena,  the 
severe  economic  hardships  experienced  as  the  result  of  occasional 
drought  and  other  adverse  meteorological  conditions,  and  the  ex- 
isting role  and  responsibilities  of  the  Federal  Government  with 
respect  to  disaster  relief,  require  appropriate  Federal  action  to 
prevent  or  alleviate  such  disasters  and  hazards ;  and 

4.  weather  modification  programs  may  have  long  range  and 
unexpected  effects  on  existing  climatic  patterns  which  are  not 
confined  by  national  boundaries.16 

By  this  act  the  Congress  proposed  "*  *  *  to  develop  a  comprehensive 
and  coordinated  national  weather  modification  policy  and  a  national 
program  of  weather  modification  research  and  development — 

1.  to  determine  the  means  by  which  deliberate  weather  modifica- 
tion can  be  used  at  the  present  time  to  decrease  the  adverse  impact 
of  weather  on  agriculture,  economic  growth,  and  the  general  pub- 
lic welfare,  and  to  determine  the  potential  for  weather  modifica- 

2.  to  conduct  research  into  those  scientific  areas  considered  most 
likely  to  lead  to  practical  techniques  for  drought  prevention  or 
alleviation  and  other  forms  of  deliberate  weather  modification; 

3.  to  develop  practical  methods  and  devices  for  weather  modifi- 
cation ; 

4.  to  make  weather  modification  research  findings  available  to 
interested  parties ; 

5.  to  assess  the  economic,  social,  environmental,  and  legal  im- 
pact of  an  operational  weather  modification  program ; 

6.  to  develop  both  national  and  international  mechanisms  de- 
signed to  minimize  conflicts  which  may  arise  with  respect  to  the 
peaceful  uses  of  weather  modification ;  and 

7.  to  integrate  the  results  of  existing  experience  and  studies  in 
weather  modification  activities  into  model  codes  and  agreements 
for  regulation  of  domestic  and  international  weather  modification 
activities." 17 

The  act  charges  the  Secretary  of  Commerce  with  responsibility  for 
conducting  "a  comprehensive  investigation  and  study  of  the  state  of 
scientific  knowledge  concerning  weather  modification,  the  present 
state  of  development  of  weather  modification  technology,  the  problems 
impeding  effective  implementation  of  weather  modification  tech- 
nology, and  other  related  matters.  Such  study  shall  include — 

(1)  A  review  and  analysis  of  the  present  and  past  research 
efforts  to  establish  practical  weather  modification  technology, 
particularly  as  it  relates  to  reducing  loss  of  life  and  crop  and  prop- 
erty destruction  ; 

(2)  A  review  and  analysis  of  research  needs  in  weather  modifi- 
cation to  establish  areas  in  which  more  research  could  be  expected 

16  Public  Law  94-490  (90  Stat.  2359),  sec.  2,  declaration  of  policy. 

« Ibid.  _ 


to,  yield  the  greatest  return  in  terms  of  practical  weather  modifi- 
cation technology ; 

(3)  A  review  and  analysis  of  existing  studies  to  establish  the 
probable  economic  importance  to  the  United  States  in  terms  of 
agricultural  production,  energy,  and  related  economic  factors 
if  the  present  weather  modification  technology  were  to  be  effec- 
tively implemented ; 

(4)  An  assessment  of  the  legal,  social,  and  ecological  implica- 
tions of  expanded  and  effective  research  and  operational  weather 
modification  projects ; 

(5)  Formation  of  one  or  more  options  for  a  model  regulatory 
code  for  domestic  weather  modification  activities,  such  code  to  be 
based  on  a  review  and  analysis  of  experience  and  studies  in  this 
area,  and  to  be  adaptable  to  State  and  national  needs ; 

(6)  Recommendations  concerning  legislation  desirable  at  all 
levels  of  government  to  implement  a  national  weather  modifica- 
tion policy  and  program ; 

(7)  A  review  of  the  international  importance  and  implications 
of  weather  modification  activities  by  the  United  States ; 

(8)  A  review  and  analysis  of  present  and  past  funding  for 
weather  modification  from  all  sources  to  determine  the  sources 
and  adequacy  of  funding  in  the  light  of  the  needs  of  the  Nation  ; 

(9)  A  review  and  analysis  of  the  purpose,  policy,  methods,  and 
funding  of  the  Federal  departments  and  agencies  involved  in 
weather  modification  and  of  the  existing  interagency  coordination 
of  weather  modification  research  efforts ; 

(10)  A  review  and  analysis  of  the  necessity  and  feasibility  of 
negotiating  an  international  agreement  concerning  the  peaceful 
uses  of  weather  modification ;  and 

(11)  Formulation  of  one  or  more  options  for  a  model  interna- 
tional agreement  concerning  the  peaceful  uses  of  weather  modifi- 
cation and  the  regulation  of  national  weather  modification-activ- 
ities ;  and  a  review  and  analysis  of  the  necessity  and  feasibility  of 
negotiating  such  an  agreement.18 

The  act  directs  each  department  and  agency  of  the  Federal  Gov- 
ernment to  furnish  pertinent  information  to  the  Secretary  of  Com- 
merce and  authorizes  the  Secretary  in  conducting  the  study  to  "solicit 
and  consider  the  views  of  State  agencies,  private  firms,  institutions 
of  higher  learning,  and  other  interested  persons  and  governmental 
entities/' 19 

A  final  report  on  the  findings,  conclusions,  and  recommendations  of 
the  required  study  is  to  be  prepared  by  the  Secretary  of  Commerce  and 
submitted  to  the  President  and  the  Congress.  The  report  is  to  include 
the  following : 

(1)  A  summary  of  the  findings  made  with  respect  to  each  of  the 
areas  of  investigation  delineated  above ; 

(2)  Other  findings  which  are  pertinent  to  the  determination 
and  implementation  of  a  national  policy  on  weather  modification; 

(3)  A  recommended  national  policy  on  weather  modification 
and  a  recommended  national  weather  modification  research  and 
development  program,  consistent  with,  and  likely  to  contribute  to, 
achieving  the  objectives  of  such  policy; 

™  Ibid.,  spc.  4.  itady. 
18  Ibid.,  sec.  5,  report. 


(4)  Recommendations  for  levels  of  Federal  funding  sufficient  to 
support  adequately  a  national  weather  modification  research  and 
development  program ; 

(5)  Recommendations  for  any  changes  in  the  organization  and 
involvement  of  Federal  departments  and  agencies  in  weather 
modification  which  may  be  needed  to  implement  effectively  the 
recommended  national  policy  on  weather  modification  and  the 
recommended  research  and  development  program ;  and 

(6)  Recommendations  for  any  regulatory  and  other  legislation 
which  may  be  required  to  implement  such  policy  and  program  or 
for  any  international  agreement  which  may  be  appropriate  con- 
cerning the  peaceful  uses  of  weather  modification,  including 
recommendations  concerning  the  dissemination,  refinement,  and 
possible  implementation  of  the  model  domestic  code  and  inter- 
national agreement  developed  under  the  specification  in  the  list  of 
investigations  above.20 

The  act  stipulated  that  the  report  was  to  be  submitted  by  the  Secre- 
tary within  1  year  after  the  date  of  enactment  of  the  law ;  that  is,  by 
October  13,  1977.  Following  a  request  by  the  Secretary  in  June  of 
1977  for  an  extension  of  this  time  allotment,  a  Senate  bill  was  intro- 
duced, providing  for  an  extension  of  the  due  date  of  the  report  through 
June  13,  1978.  No  other  action  on  this  request  was  taken,  however, 
during  the  first  session  of  the  95th  Congress.  Meanwhile,  the  study 
mandated  by  Public  Law  9J-490  continues  under  the  auspices  of  the 
Secretary  of  Commerce.21 

Congressional  direction  to  the  Bureau  of  Reclamation 

Of  special  interest  as  they  have  affected  the  weather  modification 
activities  of  the  Bureau  of  Reclamation  within  the  Department  of  the 
Interior  are  some  laws  not  specifically  concerned  with  weather  modi- 
fication as  are  the  ones  discussed  above.  The  Reclamation  Act  of  June 
17,  1902,22  directs  the  Bureau  to  develop  water  resources  for  reclama- 
tion purposes,  establishing  a  "reclamation  fund,''  which  may  be  used, 
inter  alia,  "in  the  examination  and  survey  and  for  the  construction  and 
maintenance  of  irrigation  works  for  the  storage,  diversion,  and  devel- 
opment of  waters  for  the  reclamation  of  arid  and  semiarid  lands  *  *  *" 
throughout  the  17  contiguous  Western  States  and  Hawaii.  The  author- 
ity of  the  1902  act  was  supplemented  by  the  Fact  Finders  Act  of 
December  5,  1924,  and  amendments  thereto  in  the  act  of  April  19, 
1945,23  which  enabled  the  Bureau  to  conduct  "general  investigations," 
not  related  to  specific  projects,  including  research  work,  for  the  devel- 
opment of  water  resources  without  the  necessity  of  making  the  costs 
thereof  reimbursable. 

Thus,  the  1902  Reclamation  Act,  supplemented  by  the  Fact  Finders 
Act,  provides  the  authority  for  the  Bureau  of  Reclamation  to  engage 
in  a  program  of  weather  modification  research  for  the  purpose  of  de- 
termining practical  methods  of  inducing  precipitation  and  increased 
runoff  that  can  be  stored  in  surface  reservoirs  and  used  for  "the  rec- 

» Ibid. 

21  This  study  is  underway  on  behalf  of  the  Secretary  of  Commerce  by  a  Weather  Modifica- 
tion Advisory  Board,  appointed  by  the  Secretary.  See  subsequent  discussion  of  activities  of 
the  Advisorv  Board,  beginning  p.  231. 

M  43  U.S.C.  391  et  seq. 

»  43  U.S.C.  377. 


lamation  of  arid  and  semiarid  lands/'  Funds  appropriated  for  weather 
modification  research  are  considered  expendable  on  a  nonreimbursable 

In  1961  the  Congress  specifically  directed  the  Bureau  of  Reclamation 
to  initiate  a  program  in  weather  modification  through  a  write-in  of 
$100,000  to  the  fiscal  year  190:2  Public  Works  Appropriation  Act.  This 
first  appropriation  for  the  Bureau's  weather  modification  research 
and  development  program  was  added  to  the  Appropriation  Act,  Public 
Law  87-330  (75  Stat.  722).  approved  September  30,  19(31.  in  a  con- 
gressional committee  of  conference,  under  the  heading,  "General  In- 
vestigations.'' 25  The  specific  language  which  directed  the  weather  mod- 
ification research  appeared  in  the  Senate  report  on  H.E.  9076,26  and 
the  provision  was  incorporated  into  the  conference  report  without 
mentioning  weather  modification  per  se.  The  Senate  report  included 
the  following  item : 

Increased  rainfall  by  cloud  seeding,  $100.000. — The  committee  recommends  al- 
lowance of  $100,000  to  be  used  for  research  on  increasing  rainfall  by  cloud  seed- 
ing. This  amount  would  be  utilized  in  cooperation  with  the  National  Science 
Foundation  and  the  Weather  Bureau,  which  are  expected  to  contribute  funds 
and  participate  in  this  research.27 

In  accordance  with  congressional  direction  in  the  fiscal  year  1962 
Public  Works  appropriation  bill,  the  Bureau  of  Reclamation  estab- 
lished the  Atmospheric  Water  Resources  Management  Program 
(^Project  Sky  water')  in  1962.  Since  the  start  of  this  program  con- 
gressional direction  has  continued  to  be  almost  entirely  through  pro- 
visions in  the  congressional  documents  relative  to  annual  Public  Works 
appropriations.  Appendix  J  is  a  summary  of  the  appropriation  lan- 
guage contained  in  these  documents  from  1961  through  1977,  which 
provided  such  direction.  It  may  be  noted  that  by  this  means  the  Con- 
gress has  continued  to  provide  specific  direction  to  this  program  al- 
most every  year  since  its  inception  and  has  provided  frequent  funding 
increases,  often  substantial,  over  levels  budgeted  by  the  administration. 

Legislation  providing  for  temporary  authorities  to  the  Secretary  of 
the  Interior  to  facilitate  emergency  actions  to  mitigate  impacts  of  the 
1976-77  drought  was  enacted  by  the  Congress  and  signed  by  President 
Carter  on  April  7,  1977.  Public  Law  95-18  (91  Stat.  36) ,  subsequently 
amended  by  Public  Law  95-107  (91  Stat.  870) ,  of  August  17, 1977,  pro- 
vided authority  to  appropriate  $100  million  for  a  program  including 
short-term  actions  to  increase  water  supplies,  to  improve  water  supply 
facilities,  and  to  establish  a  bank  of  available  water  for  redistribution. 
The  Bureau  of  Reclamation  published  rules  in  the  Federal  Register 
whereby  States  could  apply  for  nonreimbursable  funds  for  actions 
designed  to  augment  water  supplies.28  Under  these  provisions,  requests 
for  funds  to  support  weather  modification  activities  were  received  from 
six  States.21* 

Justus.  John  R.  and  Robert  E  .Morrison,  legislative  authority  for  atmosphere  research 
by  Federal  agencips,  tbe  Library  of  Congress,  Congressional  Research  Service,  Apr.  1,  11*77 
( unpublished),  p.  12. 

20  U.S.  Congress,  committee  of  eonferenee.  public  works  appropriation  bill.  1902;  confer- 
ence report  to  accompany  II. R.  9076.  Washington.  D.C..  U.S.  Government  Printing  Office, 
1961,  p.  24.  (87th  Cong.,  ist  sess.  House  Rept.  No.  S7-126S.) 

26  U.S.  Congress,  Senate,  Committee  on  Appropriations,  public  works  appropriation  bill, 
1962  ;  report  to  accompany  II. R.  9076.  Washington.  D.C.,  U.S.  Government  Printing  Oltice, 
1961.  p.  i>4.  (S7th  Cong..  1st  sess.  Ho.ise  Rept.  No.  87-1268.) 

■»  Ibid. 

I  -  eral  Register,  vol.  42,  No.  72.  Thursday.  Apr.  14.  1977.  pp.  19609-19613. 
20  The  States  were  California.  Colorado.  Kansas.  Nevada,  North  Dakota,  and  Utah.  ?ee 
discussion  of  the  Department  of  the  Interior  activities  in  weather  mod  iri  cat  ion.  p.  267.  for 
amounts  of  these  grants. 




Since  1947  at  least  110  bills  and  22  resolutions  dealing  specifically 
with  one  or  more  aspects  of  weather  modification  have  been  introduced 
in  the  Congress.  Moreover,  many  additional  pieces  of  proposed  legis- 
lation, providing  authorization  or  appropriations  for  broader  agency 
programs,  have  given  support  and/or  direction  to  weather  modification 
activities  within  Federal  agencies,  often  without  mentioning  such 
activities  per  se. 

Table  1  summarizes  the  legislation  and  resolutions  concerned  specifi- 
cally with  weather  modification,  which  were  proposed  from  the  first 
session  of  the  80th  Congress  to  the  first  session  of  the  95th  Congress. 
The  table  shows,  for  each  session,  the  numbers  of  bills  and  resolutions 
pertaining  to  each  of  several  aspects  of  the  subject  and  the  total  number 
of  each  introduced.  The  numbers  appearing  under  the  several  subjects 
of  weather  modification  legislation  will,  in  general,  exceed  the  total 
number  of  measures  introduced  in  a  given  year  because  many  of  the 
bills  were  concerned  with  more  than  one  aspect.  It  will  be  noted  that  a 
total  of  six  laws  were  passed  during  this  period,  as  stated  earlier.  Dur- 
ing the  93d  Congress  the  Senate  also  passed  one  resolution,  which  sup- 
ported the  position  that  the  United  States  should  seek  the  agreement 
of  other  nations  to  a  treaty  banning  environmental  modification  as  a 
weapon  of  war. 


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It  can  be  seen  from  the  table  that  congressional  activity  has  often 
evolved  in  accordance  with  the  emergence  of  various  interests  and 
issues.  Thus,  in  the  1950's  and  1960's  there  were  strong  attempts  to 
initiate  and  support  Federal  research  and/or  operational  programs, 
usually  within  one  or  another  of  several  specified  departments  or  agen- 
cies. From  time  to  time  emphasis  has  been  given  to  evaluating  weather 
modification  technology  and  establishing  a  national  policy,  usually 
:  through  mandating  an  in-depth  study ;  such  study  was  sometimes  to  be 
undertaken  by  a  select  committee  established  for  that  purpose.  In  the 
1970*3  two  thrusts  in  proposed  legislation  have  dealt  with  regulating 
and  or  licensing  of  operations  and  with  reporting  weather  modifica- 
tion activities  to  the  Federal  Government,  both  reflecting  increased 
concern  on  the  part  of  large  segments  of  the  public  about  unknown 
effects  of  such  operations  and  about  legal  and  economic  ramifications 
of  increased  or  decreased  precipitation.  Obvious  too  in  the  1970's  is  the 
reaction  of  Congress  to  public  concern  about  the  use  of  weather  modi- 
fication as  a  weapon,  as  18  resolutions  dealing  with  that  subject  were 
introduced  in  both  Houses  since  1971. 

Specific  measures  of  recent  years  on  weather  modification,  those 
introduced  in  the  94th  Congress  and  the  first  session  of  the  95th  Con- 
gress, are  summarized  in  the  following  section. 

Legislation  proposed  in  the  9J/.th  and  95th  Congress,  1st  session 

Proposed  legislation  and  resolutions  appearing  during  the  94th  Con- 
gress reflected  concern  over  many  current  problem  areas  in  weather 
modification  coming  into  focus  today,  areas  over  which  it  is  considered 
by  many  that  the  Federal  Government  should  have  some  jurisdiction. 
Based  upon  a  number  of  specific  measures  introduced  during  that  Con- 
gress and  the  ensuing  discussions  thereon,  there  emerged  the  National 
Weather  Modification  Policy  Act  of  1976  (Public  Law  94-490),  which 
could  be  a  landmark,  in  that  studies  and  decisions  pursuant  to  that  act 
may  lead  to  definition  of  a  clear  Federal  policy  for  the  first  time  in 
recent  years.  The  bills  submitted  thus  far  in  the  95th  Congress  address 
some  concerns  not  dealt  with  in  the  recent  law  and  may  presage  stipula- 
tions which  could  conceivably  be  incorporated  into  future  Federal  pol- 
icy. Undoubtedly,  the  96th  Congress  will  see  a  greater  abundance  of 
proposed  legislation  dealing  with  Federal  policy  on  weather  modifica- 
tion, following  receipt  by  the  Congress  of  the  report  from  the  Secre- 
tary of  Commerce  recommending  a  national  policy  and  a  program  of 
Federal  research  and  development.30  Measures  introduced  during  the 
94th  Congress  and  the  first  session  of  the  95th  Congress  are  summarized 
below : 

9ifh  Congress,  1st  session 

S.  2705. — To  provide  for  a  study,  within  the  Department  of 
Commerce,  by  a  National  Weather  Modification  Commission,  of 
the  research  needs  for  weather  modification,  the  status  of  current 
technologies,  the  extent  of  coordination,  and  the  appropriate 
responsibility  for  operations  in  the  field  of  weather  modification. 
(Hearing  was  held  Feb.  17, 1976.) 

S.  2706. — To  authorize  and  direct  the  Secretary  of  Commerce  to 
plan  and  carry  out  a  10-year  experimental  research  program  to 

SP  Public  Law  94-490  directs  the  Secretary  of  Commerce  to  conduct  a  study  on  weather 
modification  and  to  submit  a  report  to  the  President  and  the  Congress,  recommending  a  na- 
tional policy  and  a  program  of  Federal  research  and  development  in  weather  modification. 

34-857—79  16 


determine  the  feasibility  of  and  the  most  effective  methods  for 
drought  prevention  by  weather  modification.  Directs  the  Secre- 
tary to  appoint  an  Advisory  Board  and  provides  for  consulta- 
tion with  State  and  local  governments  starting  weather  modifica- 
tion efforts  for  drought  alleviation.  (Hearing  was  held  Feb.  17, 

S.  2707. — To  authorize  the  Secretary  of  Commerce  to  carry  out 
a  program  of  assistance  to  States  in  preventing  and  alleviating 
drought  emergencies.  (Hearing  was  held  Feb.  17, 1976.) 

H.R.  167. — To  prohibit  the  United  States  from  engaging  in 
weather  modification  activities,  including  cloud  seeding  and  fire 
storms,  for  military  purposes.  (No  action.) 

H.R.  274-2. — Directed  the  Secretaries  of  Agriculture  and  Inte- 
rior to  permit  the  conduct  of  weather  modification  activities,  in- 
cluding both  atmospheric  and  surface  activities  and  environ- 
mental research,  which  are  over,  or  may  affect,  areas  which  are 
part  of  the  National  Wilderness  Preservation  System  or  other 
Federal  lands.  Authorized  the  respective  Secretaries  to  prescribe 
such  operating  and  monitoring  conditions  as  each  deems  neces- 
sary to  minimize  or  avoid  long-term  and  intensive  local  impact 
on  the  wilderness  character  of  the  areas  affected.  (No  action.) 

H.R.  4325. — Weather  Modification  and  Precipitation  Manage- 
ment Act.  Authorized  the  Secretary  of  the  Interior  to  establish 
precipitation  management  projects  in  order  to  augment  U.S. 
usable  water  resources.  Authorized  the  Secretary  to  engage  in 
operational  demonstration  projects  for  potential  use  in  precipita- 
tion management  programs  in  certain  States  and  to  settle  and 
pay  claims  against  the  United  States  for  injury,  death,  or  losses 
resulting  from  weather  modification  pursuant  to  provisions  of 
this  act.  (No  action.) 

H.R.  4338. — Designated  specific  lands  within  the  Sequoia  and 
Sierra  National  Forests,  Calif.,  as  the  "Monarch  Wilderness," 
abolishing  the  previous  classification  of  the  "High  Sierra  Primi- 
tive Area."  Directed  the  Secretary  of  Agriculture  to  authorize  use 
of  hydrological  devices  and  to  provide  for  weather  modification 
activities  within  such  wilderness.  (No  action.) 

H.R.  10039. — Weather  Modification  Research,  Development,  and 
Control  Act  of  1975.  Directed  the  Secretary  of  Commerce  to  es- 
tablish a  weather  modification  research  and  development  pro- 
gram to  evaluate  the  specific  needs  and  uses  of  weather  modifi- 
cation and  directed  the  Secretary  to  establish  a  weather  modifica- 
tion information  system.  Prohibited  individuals  from  engaging 
in  weather  modification  activities  without  obtaining  a  permit  from 
the  Secretary  and  authorized  the  President  to  enter  into  inter- 
national agreements  to  foster  establishment  of  international  sys- 
tems for  monitoring  and  regulation  of  weather  modification  ac- 
tivities. (Joint  hearings  were  held  on  H.R.  10039  and  S.  3383, 
June  15-18, 1976 ;  no  further  action  on  H.R,  10039.) 

77.  Res,  28. — Expressed  the  sense  of  the  House  of  Rep- 
resentatives that  the  U.S.  Government  should  seek  agreement  with 
ot  her  members  of  the  United  Nations  on  the  prohibition  of  weather 


modification  as  a  weapon  of  war.  (Hearing  was  held  July  29, 1975 ; 
no  further  action.) 

H.  Res.  103.— Same  as  H.  Res.  28.  (No  action.) 

94th  Congress,  2d  Session 

S.  3383.— National  Weather  Modification  Policy  Act.  Directed 
the  Secretary  of  Commerce  to  conduct  a  comprehensive  study  of 
scientific  knowledge  concerning  weather  modification  and  tech- 
nology of  weather  modification.  Required  the  Secretary  to  prepare 
and  submit  to  the  President  and  the  Congress  a  final  report  on 
the  findings  and  conclusions  of  such  study,  including  a  recom- 
mended national  policy  on  weather  modification.  Extended 
through  fiscal  year  1980  appropriation  authorization  for  the 
weather  modification  activities  oversight  program  of  the  Depart- 
ment of  Commerce.  (Reported  to  Senate,  May  13,  1976,  in  lieu 
of  S.  2705,  S.  2706,  and  S.  2707;  considered  and  passed  by  Sen- 
ate, May  21,  1976;  hearings  held  jointly  in  House  subcommittee 
on  S.  3383  and  H.R.  10039,  June  15-18, 1976 ;  called  up  under  mo- 
tion to  suspend  the  rules,  considered,  and  passed  by  the  House, 
amended,  Sept.  20,  1976;  Senate  agreed  to  House  amendments, 
Sept.  28,  1976;  and  approved  as  Public  Law  94-490,  Oct.  13, 

H.R.  14S '44- — Extended  through  fiscal  year  1980  appropriations 
authorization  for  the  weather  modification  activities  oversight 
program  of  the  Department  of  Commerce.  ( No  action. ) 

95th  Congress,  1st  Session 

S.  1938.— To  extend  the  National  Weather  Modification  Policy 
Act  of  1976  by  extending  the  date  for  submission  of  the  required 
report  of  the  Secretary  of  Commerce  to  June  13, 1978.  (No  action.) 

H.R.  4069.— Weather  Modification  Regulation  Act  of  1977: 
Requires  weather  modification  licenses  and  permits,  establishes 
reporting  requirements  to  be  administered  by  the  Secretary  of 
Commerce,  and  requires  the  Secretary  to  establish  a  weather  mod- 
ification information  system.  Authorizes  the  President  to  enter 
into  international  agreements  to  foster  establishment  of  interna- 
tional systems  for  monitoring  and  regulation  of  weather  modifica- 
tion activities.  (No  action.) 

H.R.  4461—  Same  as  H.R.  2742,  introduced  during  94th  Con- 
gress, first  session.  (No  action.) 

H.  Res.  236. — Declares  it  to  be  the  sense  of  the  House  of  Repre- 
sentatives that  the  United  States  should  seek  an  agreement  with 
other  members  of  the  United  Nations  to  prohibit  research,  experi- 
mentation, or  the  use  of  weather  modification  as  a  weapon.  (No 
action.)  31 


Resolutions  on  toeather  modification 

As  noted  earlier,  some  22  resolutions  related  to  weather  modification 
have  been  introduced  over  the  past  30  years  in  both  Houses  of  the 
Congress.  For  convenience,  data  on  these  resolutions  are  included  along 
witli  that  on  proposed  legislation  in  table  1  and  in  the  discussion 

31  See  ch.  10  for  a  discussion  of  the  development  of  6uch  a  U.N.  convention,  opened  for 
signature  in  Geneva,  May  18.  1977. 


thereon,  and  three  resolutions  are  included  in  the  preceding  list  of 
summaries  of  weather  modification  bills  appearing  during  the  94th 
and  95th  Congresses. 

By  far,  the  largest  number  of  weather  modification  resolutions,  18 
in  all,  have  been  concerned  with  barring  the  use  of  weather  modifica- 
tion as  a  weapon  of  war.  Introduction  of  such  resolutions  began  during 
the  92d  Congress  in  1971,  and,  using  similar  language,  they  express 
the  sense  of  either  House  or  of  the  Congress  that  the  United  States 
should  seek  an  agreement  with  other  U.1\T.  members,  prohibiting  such 
use  of  environmental  modification,  including  weather  modification.  In 
1973.  the  Senate  passed  S.  Res.  71,  which  had  been  intro- 
duced by  Senator  Claiborne  Pell.  This  and  other  resolutions  urging 
prohibition  of  environmental  modification  for  purposes  of  warfare 
were  prompted  by  a  series  of  hearings  and  communications  between 
Senator  Pell  and  the  Department  of  Defense  on  the  alleged  use  of 
weather  modification  technology  as  a  weapon  in  Vietnam  by  U.S.  mili- 
tary forces.32 

Four  other  weather  modification  resolutions,  introduced  in  the  1950's 
and  1960?s,  pertained  to  the  undertaking  of  comprehensive  studies  on 
the  subject,  either  by  special  committees  to  be  established  by  the  Con- 
gress or  by  departments  and/or  agencies  of  the  executive  branch. 


Cognizant  subcommittees  of  both  Houses  have  conducted  hearings 
concerned,  at  least  in  part,  with  Federal  weather  modification  activi- 
ties, from  time  to  time  and  annually,  in  connection  with  oversight  of 
agency  programs,  authorizing  legislation,  and  annual  appropriations. 
In  addition,  more  comprehensive  hearings  on  the  subject  have  been 
important  parts  of  the  legislative  activities  leading  to  passage  of  the 
major  public  laws  on  weather  modification,  which  have  been  enacted 
since  1953. 

Of  particular  interest  in  recent  years  are  the  extensive  hearings  con- 
ducted during  1976  by  the  Subcommittee  on  Oceans  and  Atmosphere 
of  the  Senate  Committee  on  Commerce  33  and  by  the  Subcommittee  on 
the  Environment  and  the  Atmosphere  of  the  House  Committee  on 
Science  and  Technology.34  The  documents  produced  from  these  hear- 
ings contain  the  testimony  of  a  number  of  expert  witnesses  on  various 
aspects  of  weather  modification  as  well  as  reproductions  of  numerous 
pertinent  documents  which  were  incorporated  into  the  records  of  the 
hearings.  References  to  documents  on  other  weather  modification  hear- 
ings conducted  in  recent  years  are  contained  in  the  bibliography  of 
congressional  publications  in  appendix  H. 

On  October  26, 1977,  the  Subcommittee  on  the  Environment  and  the 
Atmosphere  of  the  House  Committee  on  Science  and  Technology  con- 
ducted a  special  hearing  on  the  National  Weather  Modification  Policy 
Act  of  1976  (Public  Law  94^90) .  Among  other  witnesses,  Mr.  Harlan 
Cleveland.  Chairman  of  the  Commerce  Department's  Weather  Modi- 

-'  The  correspondence  and  hearings  on  the  use  of  weather  modification  as  a  weapon  in 
Vietnam  and  of  the  development  of  a  U.N.  treaty  barring  environmental  modification  in  war- 
far*  are  discussed  among  other  international  aspects  of  weather  modification  in  ch.  10. 

"';  U.S.  Congress,  Senate.  Committee  on  Commerce.  Subcommittee  on  Oceans  and  Atmos- 
phere. Atmospheric  Research  Control  Act.  hearing.  94th  Cong.,  2d  sess.,  on  S.  2705.  S.  2706, 
and  S  2707.  Feb.  17.  1976,  Washington,  U.S.  Government  Printing  Office,  1976.  297  pp. 

M  TVS.  Congress.  House,  Committee  on  Science  and  Technology,  Subcommittee  on  the  En- 
vironment and  the  Atmosphere.  Weather  modification,  hearings,  94th  Cong..  2d  sess..  on 
TT  i:  ino?,f>  and  S.  3383,  June  15-18,  1976,  Washington,  U.S.  Government  Printing  Office, 
1976,  524  pp. 


fication  Advisory  Board,  briefed  the  subcommittee  on  progress  of  the 
Board  in  carrying  out  for  the  Secretary  of  Commerce  the  comprehen- 
sive study  required  by  the  act  and  also  reported  on  findings  of  the 
Board  to  date  in  a  discussion  paper  which  he  submitted  for  the  record.33 

Studies  and  reports  by  congressional  support  agencies 

In  addition  to  the  studies  and  reports  of  the  executive  branch  which 
were  mandated  by  the  Congress  through  legislation,  studies  have  also 
been  undertaken  on  behalf  of  the  Congress  by  congressional  support 
agencies  on  at  least  three  occasions.  The  present  report,  requested  in 
1976  by  the  Senate  Committee  on  Commerce,  was  preceded  by  a  similar 
study  and  report  requested  a  decade  earlier  by  the  same  committee.36 
In  1974,  the  General  Accounting  Office  (GAO)  conducted  a  critical 
review  of  ongoing  Federal  research  programs  in  weather  modification 
and  prepared  a  report  to  the  Congress  on  the  need  for  a  national  pro- 
gram.37 A  discussion  of  the  findings  and  recommendations  of  this  GAO 
study,  along  with  those  of  other  major  Government  and  non-Govern- 
ment studies,  is  undertaken  in  a  later  chapter  of  this  report.3S 

Activities  of  the  Executive  Branch 

The  executive  branch  of  the  Federal  Government  sponsors  nearly 
all  of  the  weather  modification  research  projects  in  the  United  States, 
under  a  variety  of  programs  scattered  through  at  least  six  departments 
and  agencies.  The  National  Atmospheric  Sciences  Program  for  19 7S  39 
includes  information  on  specific  programs  of  the  Departments  of  Agri- 
culture, Commerce,  Defense,  and  the  Interior  and  of  the  Energy  Re- 
search and  Development  Administration  (now  part  of  the  Department 
of  Energy)  and  the  National  Science  Foundation.  In  recent  years 
weather  modification  research  programs  were  also  identified  by  the  De- 
partment of  Transportation  and  the  National  Aeronautics  and  Space 

In  addition  to  specific  programs  sponsored  by  Federal  agencies,  there 
are  other  functions  relevant  to  weather  modification  which  are  per- 
formed in  several  places  in  the  structure  of  the  executive  branch.  Vari- 
ous Federal  advisory  panels  and  committees  and  their  staffs,  which 
have  been  established  to  conduct  in-dep>th  studies  and  prepare  compre- 
hensive reports,  to  provide  advice  and  recommendations,  or  to  coordi- 

35  Cleveland.  Harlan,  "A  U.S.  Policy  To  Enhance  the  Atmospheric  Environment."  A  dis- 
cussion paper  by  the  Weather  Modification  Advisory  Board,  Oct.  21,  1977.  Submitted  as  part 
of  testimonv  in  hearing:  U.S.  Congress.  House  of  Representatives,  Committee  on  Science 
and  Technology.  Subcommittee  on  the  Environment  and  the  Atmosphere,  "Weather  Modi- 
fication." 95th  Cong.,  1st  sess.,  Oct.  26,  1977,  Washington,  D.C.,  U.S.  Government  Printing 
Office,  1977,  pp.  2-49. 

36  U.S.  Library  of  Congress,  Legislative  Reference  Service,  "Weather  Modification  and  Con- 
trol," a  report  prepared  by  Lawton  M.  Hartman  and  others  for  the  use  of  the  Committee  on 
Commerce.  U.S.  Senate,  Washington,  D.C.,  U.S.  Government  Printing  Office,  Apr.  27,  1966, 
181  pp.  (89th  Cong.,  2d  sess.,  Senate  Rept.  No.  1139.) 

87  Comptroller  General  of  the  United  States,  "Need  for  a  National  Weather  Modification 
Research  Program,"  report  to  the  Congress,  U.S.  General  Accounting  Office,  Washington, 
B.C.,  Aug.  23,  1974,  71  pp. 

38  See  eh.  6.  p.  324. 

39  The  National  Atmospheric  Sciences  Program,  including  the  Federal  program  in  weather 
modification,  is  published  annually  in  a  report  of  the  Interdepartmental  Committee  for 
Atmospheric  Sciences.  The  most  recent  such  report,  containing  a  discussion  of  and  funding 
for  the  fiscal  year  1978  program  is  the  following  :  Federal  Coordinating  Council  for  Science, 
Engineering,  and  Technology.  Committee  on  Atmosphere  and  Oceans,  Interdepartmental 
Committee  for  Atmospheric  Sciences.  National  Atmospheric  Sciences  Program,  fiscal  year 
1978,  ICAS  21-FY78,  September  1977,  pp.  87-94. 


hale  Federal  weather  modification  programs  have  been  housed  and 
supported  within  executive  departments,  agencies,  or  offices.  For  exam- 
ple, the  National  Advk^iy  Committee  on  Oceans  and  Atmosphere 
(XACOA)  and  the  Weather  Modification  Advisory  Board  are  sup- 
ported through  the  Department  of  Commerce.  While  the  membership 
of  the  Interdepartmental  Committee  for  Atmospheric  Sciences 
(ICAS)  comes  from  each  of  the  Federal  departments  and  agencies 
with  atmospheric  science  programs,  its  staff  has  been  housed  in  the 
National  Science  Foundation. 

The  program  whereby  Federal  and  non-Federal  U.S.  weather  mod- 
ification activities  are  reported  to  the  Federal  Government  is  adminis- 
tered by  the  National  Oceanic  and  Atmospheric  Administration 
(XOAA)  within  the  Department  of  Commerce.  Under  this  program  a 
central  file  is  maintained  on  all  such  projects  in  the  United  States, 
and  summary  reports  on  these  projects  are  published  on  a  nearly 
annual  basis  by  NOAA. 

The  United  States  has  been  active  in  at  least  two  areas  of  interna- 
tional interest  in  weather  modification.  One  aspect  has  been  the  efforts 
through  the  United  Nations  to  promote  the  adoption  of  a  treaty  bar- 
ring weather  modification  as  a  military  weapon.  There  is  also  a  U.S. 
interest  in  international  efforts  to  modify  the  environment  for  bene- 
ficial purposes.  The  State  Department  is  active  in  negotiating  agree- 
ments with  other  countries  which  might  be  affected  by  U.S.  experiments 
and  has  also  arranged  for  Federal  agencies  and  other  U.S.  investiga- 
tors for  participation  in  international  meterological  projects,  includ- 
ing weather  modification,  under  the  World  Meteorological  Organiza- 
tion (WMO).  These  activities  are  discussed  in  more  detail  in  a  subse- 
quent chapter  on  international  aspects  of  weather  modification.40 

In  the  next  subsection  there  is  an  attempt  to  describe  the  Federal 
organizational  structure  for  weather  modification,  at  least  to  the  extent 
that  such  a  structure  exists,  has  existed,  or  may  exist  in  the  near 
future.  Other  subsections  address  Federal  coordination  and  advisory 
groups,  the  weather  modification  activities  reporting  program,  and 
the  array  of  Federal  studies  and  reports  which  have  been  undertaken 
by  the  executive  branch,  either  as  required  by  law  or  initiated  within 
the  branch.  A  summary  of  the  Federal  research  program  and  detailed 
descriptions  of  each  of  the  several  agencies  programs  in  weather  modi- 
fication are  contained  in  a  separate  major  section  at  the  end  of  this 



Cum  nt  status  of  Federal  organization  for  weather  modification 

The  present  Federal  structure  of  weather  modification  research 
activities  is  characterized  esseiitially  by  the  mission-oriented  approach, 
where  each  of  six  or  seven  deportments  and  agencies  conducts  its 
own  program  in  accordance  with  broad  agency  goals  or  under  specific 
directions  from  the  Congress  or  the  Executive.  The  exception  to  this 
approach  is  the  program  of  the  Xational  Science  Foundation,  whose 
funded  weather  modification  research  activities  have  included  a  broad 

<°  Spp  en  i  o. 
11  See  p.  241  ff. 


range  of  individual  fundamental  problem  investigations,  research 
supporting  some  aspects  of  the  project  of  other  Federal  agencies, 
and  conduct  of  major  projects  initiated  by  the  Foundation.  The  pro- 
grams of  the  several  agencies  have  been  loosely  coordinated  with  others 
through  various  independent  arrangements  and/or  advisory  panels 
and  particularlv  through  the  Interdepartmental  Committee  for  At- 
mospheric Sciences  (ICAS).  The  ICAS,  established  in  1959  by  the 
former  Federal  Council  for  Science  and  Technology,  provides  advice 
on  matters  related  to  atmospheric  science  in  general  and  has  also  been 
the  principal  coordinating  mechanism  for  Federal  research  in  the 
field  of  weather  modification.  The  following  observation  on  the  cur- 
rent Federal  weather  modification  organizational  structure  was  stated 
recently  by  the  chairman  of  the  ICAS  : 

Organization [s]  doing  the  research  [should]  be  knowledgeable  of  the  sector 
of  the  public  that  is  to  be  involved  with  special  weather  modification  techniques. 
There  is  no  single  agency  within  the  Government  that  knows  all  of  the  problems 
of  society  vis-a-vis  weather  modification.  As  things  stand,  the  individual  weather 
modification  programs  being  carried  out  by  the  various  ICAS  member  agencies 
are  being  pursued  in  concert  with  the  missions  of  those  agencies.42 

The  nature  of  the  present  Federal  organizational  structure  for 
weather  modification  is  related  to  and  results  from  the  prevailing 
policy,  or  lack  of  such  policy,  currently  subscribed  to  by  the  Federal 
Government  regarding  weather  modification.  The  clearest  statement 
of  such  a  policy  came  in  a  reply  to  a  1975  letter  from  Congressmen 
Gilbert  Gude  and  Donald  M.  Fraser  and  Senator  Claiborne  Pell, 
addressed  to  the  President,  urging  that  a  coordinated  Federal  program 
in  the  peaceful  uses  of  weather  be  initiated.43  In  the  official  response 
from  the  executive  branch,  written  by  Norman  E.  Ross,  Jr.,  Assistant 
Director  of  the  Domestic  Council,  the  current  Federal  weather  modifi- 
cation policy  was  affirmed : 

We  believe  that  the  agency  which  is  charged  with  the  responsibility  for  deal- 
ing with  a  particular  national  problem  should  be  given  the  latitude  to  seek 
the  best  approach  or  solution  to  the  problem.  In  some  instances  this  may  involve 
a  form  of  weather  modification,  while  in  other  instances  other  approaches  may 
be  more  appropriate. 

While  we  would  certainly  agree  that  some  level  of  coordination  of  weather 
modification  research  efforts  is  logical,  we  do  not  believe  that  a  program  under 
the  direction  of  any  one  single  agency's  leadership  is  either  necessary  or 
desirable.  We  have  found  from  our  study  that  the  types  of  scientific  research 
conducted  by  agencies  are  substantially  different  in  approach,  techniques,  and 
type  of  equipment  employed,  depending  on  the  particular  weather  phenomena 
being  addressed.  *  *  *  Each  type  of  weather  modification  requires  a  different  form 
of  program  management  and  there  are  few  common  threads  which  run  along 
all  programs.44 

Recently,  the  Chairman  of  the  Commerce  Department's  Weather 
Modification  Advisory  Board,  Harlan  Cleveland,  expressed  the 
Board's  opinion  of  the  current  Federal  policy  and  structure  : 

The  United  States  does  not  now  have  a  weather  modification  policy.  The 
three  main  Federal  actors  in  weather  modification  research  are  NOAA  in  the 

42  Testimony  of  Dr.  Edward  P.  Todd  In  U.S.  Congress,  House  of  Representatives,  Commit- 
tee on  Science  and  Teehnolosy,  Subcommittee  on  the  Environment  and  the  Atmosphere, 
'Weather  Modification."  hearings.  94th  Cong.,  2d  sess..  June  15-18,  1976.  Washington.  D.C., 
T.S.  Government  Printing  Office,  1976,  p.  81. 

43  Gude.  Gilbert.  "Weather  Modification."  Congressional  Record.  June  17.  1975,  pp.  19201- 
192f>3.  (The  statement  in  the  Congressional  Record,  including  the  letter  to  the  President 
and  the  official  reply,  are  reproduced  in  app.  A.) 

"  Ibid. 


Department  of  Commerce,  the  Bureau  of  Reclamation  in  the  Department  of 
the  Interior,  and  the  National  Science  Foundation.  . . .  Their  combined  R  and  D 
efforts  can  only  be  described  as  fragmented  and  famished,  living  from  hand  to 
mouth  on  each  agency's  relationship  with  a  different  congressional  subcommittee, 
with  no  sense  of  a  national  policy  or  program.  .  .  .  The  agencies  that  are  involved, 
and  their  university  and  other  contractors  and  grantees,  have  developed,  despite 
the  fragmentation,  remarkably  effective  informal  relationships  which  make 
the  coordination  and  mutual  assistance  better  than  the  division  of  roles  and 
missions  would  indicate.45 

A  somewhat  different  viewpoint,  but  related  in  several  points  to  the 
preceding  opinions  w*as  expressed  in  1976  by  Dr.  Ronald  L.  Lavoie, 
Director  of  NOAA's  Environmental  Modification  Office,  addressing 
the  second  meeting  of  the  North  American  Interstate  Weather  Modifi- 
cation Council : 

Let  me  address  the  question  of  current  Federal  policies  in  weather  modifi- 
cation— the  statement  has  been  made  that  there  aren't  any.  I  think  that  I  must 
disagree  with  that  statement.  There  are,  in  fact,  such  policies  although  they 
are  perhaps  unobtrusive  or  low-key.  They  certainly  aren't  propounded  very 
loudly,  but  I  think  it  is  safe  to  say  that  there  is  some  Federal  policy  on  weather 
modification.  .  .  .  For  example,  in  the  area  of  research  and  operations  the  Federal 
policy,  or  you  may  call  it  strategy,  is  to  leave  it  to  the  specialized  agencies  to 
fund  research  and  to  develop  or  apply  weather  modification  in  carrying  out  their 
particular  missions.  One  can  argue  with  this  policy ;  nevertheless,  it  does 
exist.  .  .  .  One  shouldn't  get  the  impression,  however,  that  this  is  an  entirely 
fragmented  effort.  .  .  .  There  is  some  coordination  or  integration,  at  least  in  the 
sense  that  technocrats  responsible  for  advising  the  agencies  in  these  matters  get 
together  to  discuss  issues  and  share  problems  Nevertheless,  there  is  no  Fed- 
eral or  national  commitment  to  weather  modification,  and  I  believe  that  this  is 
what  was  implied  when  it  was  said  that  there  was  no  national  policy.*8 

Yet  another  observation  on  the  subject  of  Federal  organization  is 
that  expressed  in  the  1974  report  by  the  U.S.  General  Accounting 

Our  review  of  the  Federal  weather  modification  research  activities  supports 
the  findings  of  nearly  a  decade  of  studies.  These  studies  conducted  by  scientific 
panels,  committees,  and  other  groups  all  identified  common  problems — ineffec- 
tive coordination,  fragmented  research,  and  research  efforts  that  are  subcritical 
(funded  below  the  level  necessary  to  produce  timely,  effective  results).  Most 
studies  proposed  a  common  solution.  What  was  needed,  in  essence,  was  a 
national  research  program  under  a  single  Federal  agency  responsible  for  estab- 
lishing plans  and  priorities,  obtaining  the  needed  funds  from  the  Congress, 
managing  research  efforts,  and  accounting  for  the  results  its  programs  achieved. 

To  date,  except  for  the  establishment  of  several  coordinating  committees, 
subcommittees,  and  advisory  panels — none  of  which  have  the  authority  to  take 
action  to  correct  problems  already  identified — an  effective  overall  national 
weather  modification  research  program  has  not  been  established.47 

There  is  some  consensus  that  the  apparent  fragmentation  and  lack 
of  a  cohesive  Federal  effort  have  not  only  prevented  the  growth  of  a 
strong,  adequately  funded  research  program  but  may  have  also 
retarded  progress  in  development  of  weather  modification  technology 

45  Cleveland,  Harlan.  "A  U.S.  Policy  To  Enhance  the  Atmospheric  Environment."  A  dis- 
cussion paper  by  the  Weather  Modification  Advisory  Board,  Oct.  21,  1977.  (Submitted  as 
part  of  testimony  in  hearing  :  U.S.  Congress,  House  of  Representatives,  Committee  on  Sci- 
ence and  Technology.  Subcommittee  on  the  Environment  and  the  Atmosphere,  "Weathel 
Modification,"  Oct.  26,  1977.  p.  41.) 

49  Lavoie,  Ronald  L..  "Effects  of  Legislation  on  Federal  Programs  and  the  Prospect  of  Fed- 
eral Involvement."  In  proceedings  of  Conference  on  Weather  Modification,  Today  and  Tomor- 
row :  second  annual  meeting  of  the  North  American  Interstate  Weather  Modification  Coun- 
cil, Kansas  City,  Mo.,  Jan.  15-16.  1976,  pub.  No.  76-1,  pp.  56-57. 

*"  Comptroller  General  of  the  United  States.  "Need  for  a  National  Weather  Modification 
Research  Program."  report  to  the  Congress.  U.S.  General  Accounting  Oftlce,  B-133202,  Wash- 
ington, D.C.,  Aug.  23,  1974,  p.  3. 


itself.  Many  feel  strongly  that  assignment  of  a  "lead  agency"  would 
solidify  and  strengthen  the  Federal  effort.  To  others,  however,  "*  *  * 
the  present  structure  for  Federal  Government  activity  in  weather  mod- 
ification appears  to  be  working  satisfactorily,"  48  and  the  existence  of 
separate  agency  programs  fosters  increased  understanding  through 
independent  research  projects  and  through  the  cross- fertilization  of 
ideas  and  exchange  of  findings  achieved  in  cooperative  projects,  in 
professional  meetings,  and  through  program-level  coordination. 

In  a  recent  Federal  study  on  weather  modification,  a  subcommittee 
of  the  Domestic  Council  could  not  reach  a  consensus  on  the  proper 
institutional  structure  for  planning  and  management  of  the  national 
weather  modification  research  effort.  Consequently,  both  of  the  posi- 
tions noted  above  were  identified  as  options  for  such  Federal 
structure : 49 

Option  (1)  :  Continue  coordination  and  planning  of  the  national 
weather  modification  effort  through  the  Interdepartmental  Committee 
for  Atmospheric  Sciences  of  the  Federal  Council  for  Science  and 
Technology,  with  individual  agencies  pursuing  their  mission  responsi- 

Option  (2)  :  Establish  a  lead  agency  to  foster  the  broad  advance- 
ment of  the  science  and  technology  of  weather  modification  as 
recommended  by  the  National  Advisory  Committee  on  Oceans  and 
Atmosphere,  the  National  Academy  of  Sciences,  and  other  groups  to 
coordinate  and  plan  the  national  effort  with  the  assistance  and  partici- 
pation of  other  agencies. 

Those  who  espouse  the  latter  position  feel  that  the  lead  agency 
responsibility  should  include  the  following  functions : 50 

The  lead  agency  would  assume  the  leadership  for  planning  the 
Federal  weather  modification  program,  in  concert  with  those  other 
concerned  agencies,  universities,  and  the  private  sector. 

The  lead  agency  would  present,  within  the  executive  branch,  a 
consolidated  national  weather  modification  research  plan  and  be 
available  to  represent  the  national  plan  before  the  Congress. 

The  lead  agency  would,  within  the  framework  of  the  joint  plan- 
ning effort,  encourage  and  assist  in  justifying  programmatic  ac- 
tivities in  other  agencies  that  might  contribute  significantly  to  the 
national  weather  modification  objectives,  especially  when  those 
programs  can  be  implemented  as  supplements  to  the  agencies' 
ongoing  mission-related  activities. 

The  lead  agency  would  take  on  the  responsibility  for  presenting 
the  budgetary  requirements  to  carry  out  the  national  plan  to  the 
Office  of  Management  and  Budget  and,  with  due  consideration  of 
overall  priorities  of  the  agency,  would  seek  to  provide  within  its 
own  budget  for  activities  essential  to  the  national  plan  and  not 
incorporated  in  the  budgets  of  the  other  agencies. 
The  history  of  the  organization  of  the  Federal  program  in  weather 
modification,  to  the  extent  that  such  a  structure  has  existed,  can  be 

4*  Testimony  of  Dr.  Alfred  J.  Esgers.  Jr..  Assistant  Director  for  Research  Applications, 
National  Science  Foundation  in  U.S.  Congress.  House  of  Representatives.  Committee  on 
Seienr-e  and  Technology.  Subcommittee  on  the  Environment  and  the  Atmosphere.  "Weather 
Modification. "  v>earin£s.  04th  Consr..  2d  sess.,  June  15-1S,  1976,  Washington,  D.C.,  U.S.  Gov- 
ernment Printing:  Office.  1976.  p.  109. 

49  U.S.  Domestic  Council.  Environmental  Resources  Committee.  Subcommittee  on  Climate 
Change,  "The  Federal  Role  in  Weather  Modification."  Washington,  D.C,  December  1975, 
p.  19. 

60  Ibid.,  app.  A,  pp.  A-2  and  A-3. 


conveniently  divided  into  three  periods,  each  roughly  a  decade  long. 
These  periods  and  the  characteristics  of  the  Federal  organization  dur- 
ing each  are  discussed  briefly  below. 

Federal  structure;  194-6-57 

As  seen  in  the  earlier  historical  account  of  weather  modification,  in 
the  period  from  1946  through  1957  practically  all  projects  in  the 
United  States  were  conducted  by  private  individuals  and  by  industry 
supported  through  private  funds.  What  activities  the  U.S.  agencies 
did  support  were  both  mission  oriented  and  mostly  uncoordinated.  The 
Defense  Department  developed  an  early  research  program,  specifically 
in  seeding  technology  and  hardware.  Since  World  War  II,  the  Air 
Force  had  a  continuing  need  to  dissipate  fog,  and  the  Korean  war  and 
SAC  missions  during  this  period  required  airports  to  be  open  to  permit 
unrestricted  flights.  The  Navy  developed  a  strong  research  capability 
at  its  China  Lake,  Calif.,  laboratory,  concentrating  on  seeding  de- 
vices and  materials.  Project  Cirrus,  a  joint  project  of  the  Army  Signal 
Corps,  the  Navy,  and  the  Air  Force,  was  initiated  by  the  Defense 
Department  in  1947  and  continued  through  1952. 

Civilian  implications  for  weather  modification  were  investigated 
by  the  U.S.  Weather  Bureau  of  the  Commerce  Department  in  1948  as 
part  of  its  cloud  physics  program.  The  Bureau's  early  position,  how- 
ever, seemed  to  lack  enthusiasm  for  a  research  program  at  the  time, 
largely  reflecting  agency  conservatism  and  some  unwillingness  to  be 
caught  up  in  a  technology  that  was  fraught  with  exaggerated  claims 
of  commercial  rainmakers.51  This  early  negative  outlook  of  the 
Weather  Bureau  was  modified  in  the  late  1960's  when  its  successive 
parent  organizations,  the  Environmental  Science  Services  Adminis- 
tration (ESSA)  and  the  National  Oceanic  and  Atmospheric  Admin- 
istration (NOAA),  inaugurated  a  fresh  interest  in  a  weather  modifi- 
cation research  program.  The  Weather  Bureau  did  participate  with 
the  Navy  in  project  SCUD  in  1953-54  along  the  east  coast,  in  an 
attempt  to  modify  the  behavior  of  extratropical  cyclones  by  artificial 

The  third  Federal  agency  conducting  weather  modification  re- 
search during  this  period  was  the  Forest  Service  of  the  U.S.  Depart- 
ment of  Agriculture,  which  in  1953  initiated  Project  Skyfire,  aimed 
at  suppressing  lightning,  a  major  cause  of  forest  fires.  This  project 
received  joint  support  later  during  the  1960's  from  the  National  Sci- 
ence Foundation,  and.  until  its  demise  in  1976.  was  the  longest  run- 
ning single  Federal  weather  modification  research  project. 

Confusion  and  uncertainty  in  the  state  of  weather  modification, 
owing  to  a  mixed  reaction  to  achipA-oments  and  claims  of  achieve- 
ment of  weathor  modification  operators  and  to  the  lack  of  a  cohesive 
research  program  in  the  Federal  Government,  led  to  the  establish- 
ment in  1953  of  the  Advisory  Committee  on  Weather  Control,  by 
Public  Law  83-256.  During  the  conduct  of  the  intensive  investiga- 
tion of  the  subject  by  the  Advisory  Committee  between  1953  and 

r>1  Communications  from  F.  W.  Reichelderfer.  Chief  of  the  U.S.  Weather  Bureau,  in  U.S. 
Congress.  Senate.  Committees  on  Interior  and  Insular  Affairs.  Interstate  and  Foreign  Com- 
merce, and  Agriculture  and  Forestry,  "Weather  Control  and  Augmented  Potable  Water 
Supply,"  Joinl  hearings,  ,92d  Cong.,  1st  sess..  Mar.  14.  15,  16,  19  and  Apr.  5,  1951,  Washing- 
ton, D.C.,  U.S.  Government  Printing  Office,  1951,  pp.  37^17. 


1957.  the  committee  seems  to  have  provided  somewhat  of  a  coordina- 
tion function  and  even  some  modicum  of  direction  to  the  Federal 
effort  it  was  studying.  There  was  support  in  the  Congress  for  both 
the  formulation  and  the  Federal  management  by  the  Advisory  Com- 
mittee of  a  5-year  Federal-State  weather  modification  research  pro- 
gram, to  be  conducted  by  the  committee,  the  States,  universities,  and 
private  institutions.52  The  Advisory  Committee  favored  an  existing 
Federal  agency,  however,  for  this  proposed  management  function. 

Federal  structure;  1958-68 

The  Advisory  Committee,  reporting  in  1957,  provided  a  setting 
for  progress  over  the  next  10  years,  as  it  presented  elements  of  a 
national  policy  and  guidelines  for  future  development  of  a  research 
program.  A  former  NSF  program  manager  for  weather  modifica- 
tion, Earl  G.  Droessler,  recently  praised  the  work  of  the  Advisory 
Committee : 

The  Committee  did  a  remarkable  job  for  weather  modification.  Perhaps,  most 
importantly,  its  careful  study  and  reporting  in  the  1950's  gave  a  measure  of 
respect,  cohesion,  and  momentum  for  the  field  of  weather  modification,  and 
thus  provided  a  setting  for  progress  over  the  next  decade  and  more.  Prior  to 
the  work  of  the  committee,  the  field  was  plagued  with  tension  and 

Encouraging  a  wide  research  program  in  meterology  as  the  essen- 
tial foundation  for  understanding  weather  modification,  the  Ad- 
visory Committee  named  the  National  Science  Foundation  as  its  rec- 
ommended agency  for  sponsoring  the  required  research  program. 
Accordingly,  the  Congress,  when  it  enacted  Public  Law  85-510,  di- 
rected the  NSF  to  initiate  and  support  a  program  in  weather  modi- 
fication and  effectively  named  the  NSF  as  lead  Federal  agency  for 
weather  modification. 

Weather  modification  research  enjoyed  a  position  of  high  value 
and  priority  among  the  top  leadership  of  the  Foundation.54  The  XSF 
promoted  a  vigorous  research  program  through  grants  to  universi- 
ties, scientific  societies  and  the  National  Academy  of  Sciences,  in- 
dustry, and  agencies  of  the  Federal  Government  and  established 
an  Advisory  Panel  for  Weather  Modification,  which  reported  to 
the  Foundation.  A  series  of  10  annual  reports  on  weather  modifica- 
tion were  published  by  the  NSF  for  fiscal  years  1959  through  1968. 
Recognizing  the  severe  shortage  of  trained  personnel,  the  NSF  es- 
tablished the  policy  of  financing  graduate  and  postgraduate  train- 
ing as  part  of  its  grant  support  program,  stating  in  its  second  annual 
report,  "In  the  field  of  weather  modification  our  greatest  deficiency 
today  is  skilled  manpower."  55 

At  the  working  level,  representatives  of  nine  Government  agencies 
were  called  together  by  the  NSF  to  form  the  Interagency  Conference 
on  Weather  Modification  to  afford  a  mechanism  for  communication  on 
weather  modification  activities  and  to  plan  and  develop  cooperative 

32  See.  for  example.  S.  86  and  companion  House  bills.  H.R.  3631.  H.R.  '5232,  H.R.  5954, 
and  H.R.  5958.  introduced  in  the  85th  Congress  during  1957. 

53  Droessler.  Earl  G..  "Weather  Modification  :  Federal  Policies.  Funding  from  all  Sources, 
Interagency  Coordination,"  background  paper  prepared  for  the  U.S.  Department  of  Com- 
merce Weather  Modification  Advisorv  Board.  Raleigh,  N.C.,  Mar.  1,  1977,  p.  1. 

"Ibid.,  p.  2. 

5r>  National  Science  Foundation.  "Weather  Modification  ;  Second  Annual  Report  for  Fiscal 
Year  ended  June  30,  1960."  Washington.  D.C..  U.S.  Government  Printing  Office,  June  16, 
1961.  p.  1. 


projects.56  Joint  Federal  projects  were  established  between  the  Foun- 
dation- and  the  Departments  of  Agriculture,  Commerce,  and  Interior. 
During  this  period  the  Congress,  wanting  to  support  more  applied  re- 
search directed  toward  a  major  problem,  such  as  requirements  for  more 
precipitation  in  the  West,  appropriated  funds  for  what  was  to  become 
a  major  weather  modification  program  under  the  Bureau  of  Reclama- 
tion in  the  Department  of  the  Interior.  The  Foundation  warmly  en- 
dorsed the  Bureau  of  Reclamation's  "Project  Sky  water"  and  has  since 
funded  many  of  the  research  projects  associated  with  this  program.57 

Fi  deral  structure;  1968-77 

The  lead  agency  responsibilities  and  authorities  of  the  National 
Science  Foundation  acquired  in  1958  under  Public  Law  85-510  were 
abrogated  by  Public  Law  90-407,  enacted  July  18, 1968,  which  became 
effective  September  1,  1968.  A  lapse  in  Federal  policy  and  Federal 
structure  has  since  occurred  as  a  result  of  congressional  and  executive 
inaction,  although  after  a  hiatus  of  over  3  years,  some  responsibility 
was  given  to  XOAA  in  1971;  namely,  that  for  collecting  and  dis- 
seminating information  on  weather  modification  projects  in  the  United 
States.  This  requirement,  directed  by  Public  Law  92-205,  of  Decem- 
ber 18, 1971,  has  been  the  single  Federal  weather  modification  function 
prescribed  by  law  until  1976,  when  Public  Law  94-490  required  the 
Secretary  of  Commerce  to  conduct  a  study  to  recommend  a  national 
policy  and  a  research  program  in  weather  modification.  The  lead 
agency  responsibility  has  never  been  reassigned,  and  Federal  leader- 
ship for  research  purposes  is  dispersed  among  the  several  agencies. 

The  only  semblance  of  weather  modification  leadership  in  the  Fed- 
eral structure  during  this  period  has  been  through  the  coordination 
mechanism  of  the  Interdepartmental  Committee  for  Atmospheric  Sci- 
ences (ICAS).  The  ICAS  has  established  some  policy  guidelines  and 
has  sponsored  activities,  such  as  the  annual  interagency  weather  modi- 
fication conferences,  intended  to  foster  cooperation  among  agency 
programs.  It  has  not  assumed  a  management  role  nor  has  it  sought  to 
intervene  in  the  budgeting  processes  by  which  the  several  agency  pro- 
grams are  supported.  The  activities  of  the  ICAS  are  discussed  in  more 
detail  in  a  section  to  follow  on  coordination  of  Federal  weather  modi- 
fication activities. 

Future  Federal  organization  for  weather  modification 

The  present  intensive  study  underway  within  the  Department  of 
Commerce,  as  directed  by  the  National  Weather  Modification  Policy 
Act  of  1976,  Public  Law  94-490,  mav  be  laying  the  groundwork  for  a 
clear  Federal  policy  in  weather  modification,  after  a  10-year  lapse  in 
Federal  leadership  and  two  decades  after  the  first  major  Federal 
wpp.ther  modification  study  wns  submitted  to  the  President  and  the 
Concrress.  The  new  approach  will  benefit  from  scientific  and  technical 
advnn^os  as  well  as  the  greater  attention  which  has  been  given  in  recent 

54  t<  n  annual  interaerpnev  conferences  on  weather  modification  wore  sponsored  by  the 
National  Seience  Foundation  throujrh  10f»S.  Since  that  year,  when  the  lead  asrency  role  was 
fn1-Pn  from  t|lfl  -yQ-p  r,v  public  Law  00  407.  the  annual  interagency  conference  has  been 
sponsored  by  the  Interdepartmental  Committee  for  Atmospheric  Sciences  (TCAS>.  The  11th 
conference  sponsored  by  ICAS.  was  conducted  by  the  NSF  at  t^e  request  of  ICAS  :  banning 
with  tbe  12th.  the  annual  conference  have  been  conducted  by  NO  A  A.  at  the  request  of  ICAS, 

th%°PrC^ess1  — "^Weather  Modification:  Federal  Policies,  Funding  from  all  Sources,  Inter- 
agency  Coordination,"  1977,  p.  4. 


years  to  legal,  social,  economic,  ecological,  and  international  aspects 
of  the  subject.  Part  of  the  national  policy  which  will  presumably  be 
established  by  the  Congress  following  the  study  (very  likely  during 
the  96th  Congress)  will  be  a  reorganized  or  reconstituted  Federal 
structure  for  leading  and  managing  the  Federal  activities  in  weather 

Kecognizing  that  most  studies  of  the  past  decade  have  proposed  solv- 
ing the  apparent  fragmentation  of  Federal  projects  and  responsibil- 
ities by  redesignating  a  lead  agency,  and  also  observing  some  of  the 
objections  and  shortcomings  of  such  a  designation,  the  Commerce  De- 
partment's Weather  Modification  Advisory  Board  has  considered  vari- 
ous options  for  structuring  the  Federal  program.  One  possible  option 
the  Board  is  considering  in  its  study  is  the  creation  of  a  special  agency 
for  weather  modification,  "with  a  mandate  to  learn  what  needs  to  be 
learned  about  weather  modification  and  to  insure  regulation  of  its 
practice,"  58  The  new  agency  would  "plan,  budget,  spur,  supervise,  and 
continually  evalute  a  Federal  program  of  research  and  development, 
designed  to  enhance  the  atmospheric  environment."  Under  this  concept 
existing  agency  projects  would  become  part  of  a  coordinated  Federal 
effort,  and  future  projects  would  be  presented  to  the  Congress  and  to 
the  Executive  "as  an  understandable  part  of  a  coherent  R  and  D 
strategy."  59 

The  Advisory  Board  has  had  difficulty  in  deciding  where  such  a  new 
agency  should  be  placed  in  the  executive  structure.  Presumably  it  could 
be  made  part  of  an  existing  structure  or  it  could  be  established  as  a 
"semi-autonomous"  agency  attached  to  an  existing  department  for  ad- 
ministrative purposes  and  support.  With  the  creation  of  a  Department 
of  Natural  Resources,  as  has  been  proposed,  a  logical  departmental 
home  for  the  suggested  weather  modification  agency  would  be  found. 
The  Board  further  suggests  that  such  a  new  agency,  regardless  of  its 
location  in  the  Federal  structure,  should  work  closely  with  a  small 
(five-  to  nine-member)  Advisory  Board,  composed  of  people  ac- 
quainted with  atmospheric  sciences,  user  needs,  operational  realities, 
advantages  of  costs  and  benefits,  and  "the  broader  national  and  inter- 
national issues  involved."  60 

The  current  thinking  of  the  Weather  Modification  Advisory  Board 
also  includes  a  laboratory  center  as  part  of  the  proposed  new  agency, 
one  newly  established  or  an  existing  Federal  laboratory  converted  to 
weather  modification  research.  While  some  research  and  development 
would  be  conducted  "in  house"  by  the  agency,  portions  of  the  coordi- 
nated research  effort  would  be  allocated  to  other  Federal  agencies  or  by 
contract  to  universities  and  other  non-Federal  institutions.61 

Droessler  has  also  observed  increased  individual  support  for  the  con- 
cept of  a  weather  modification  national  laboratory.  lie  suggests  that 
the  location  of  such  a  center  in  the  Federal  structure  should  be  deter- 
mined by  its  principal  research  thrust.  If  basic  scientific  research,  such 
as  that  which  "undergirds"  weather  modification  applications,  is  pri- 
mary, he  suggests  that  NSF  should  have  the  responsibility.  If  the  focus 
of  the  new  proposed  laboratory  should  be  on  severe  storm  amelioration, 

58  Cleveland,  "A  U.S.  Policy  to  Enhance  the  Atmospheric  Environment,"  discussion  paper 
by  thp  Weather  Modification  Advisorv  Board.  Oct.  21,  1977,  pp.  23-24. 
69  Ibid.,  p.  24. 

60  Ibid. 

61  Ibid.,  p.  25. 


including  hurricane  research,  NO AA  should  be  the  management  choice. 
Finally,  if  research  of  the  new  laboratory  is  aimed  toward  the  impacts 
of  weather  modification  on  agriculture,  the  U.S.  Department  of  Agri- 
culture should  be  directed  to  establish  and  manage  the  facility.62 

A  number  of  bills  were  introduced  in  the  Congress  from  time  to  time 
which  would  have  established  within  one  agency  or  another  a  single 
agency  with  responsibility  for  managing  a  Federal  weather  modifica- 
tion program.  For  example,  S.  2875  in  the  89th  Congress  would  have 
created  in  the  Department  of  the  Interior  a  central  scientific  and  en- 
gineering facility  and  regional  research  and  operations  centers.  In  the 
same  Congress,  S.  2916,  which  did  pass  the  Senate,  would  have  pro- 
vided much  the  same  structure  within  the  Department  of  Commerce. 
Both  bills  permitted  weather  modification  research  in  support  of  mis- 
sions by  the  other  Federal  agencies,  but  established  a  focal  point  for 
research  and  for  other  management  functions  in  the  Department  of  the 
Interior  or  the  Department  of  Commerce,  respectively.63 

In  addition  to  management  of  Federal  research  programs  and  co- 
ordination of  these  programs,  the  Federal  weather  modification  orga- 
nizational structure  must  also  be  concerned  with  other  functions.  These 
could  include  planning,  project  review,  data  collection  and  monitoring, 
regulation,  licensing,  and  indemnification.  The  institutional  arrange- 
ment within  which  these  activities  are  handled  could  be  part  of  the 
agency  with  prime  research  responsibility,  or  some  or  all  of  these  func- 
tions could  be  assigned  elsewhere.  For  example,  the  State  Department 
will  presumably  continue  to  exercise  appropriate  authorities  with 
regard  to  international  programs  or  U.S.  programs  with  potential 
impacts  on  other  nations,  though  responsibility  for  cooperation  on 
the  scientific  and  technical  aspects  of  such  projects  would  quite  natur- 
ally be  given  to  one  or  more  research  agencies.  Assignment  of  some  of 
these  functions  might  be  to  other  agencies  or  to  special  commissions, 
established  as  in  some  States,  to  deal  with  regulation,  licensing,  and 

Grant  argues  that  "the  extensive  multidisciplinary  nature  of  and 
the  potential  impact  on  large  segments  of  society  by  weather  modifica- 
tion demands  great  breadth  in  the  organizational  structure  to  manage 
the  development  of  weather  modification."  64  He  continues : 

In  view  of  these  complex  involvements  and  interactions,  it  is  clear  that  the 
governmental  organizational  structure  needs  to  he  much  broader  than  the  mis- 
sion interests  of  the  respective  Federal  agencies.  Presently,  coordination  is 
effected  through  ICAS.  More  is  required.  The  present  program  in  weather  modi- 
fication is  too  fragmented  for  optimal  utilization  of  resources  to  concentrate  on 
all  aspects  of  the  priority  problems.  Weather  modification  has  not  moved  to  the 
stage  where  research  should  be  concentrated  in  the  respective  mission  agencies. 

Many  of  the  priorities  and  problems  are  basic  to  weather  modification  itself 
and  must  l>e  resolved  and  tested  before  emphasis  is  placed  on  the  respective  mis- 

62  Droessler,  "Weather  Modification  :  Federal  Policies,  Funding  From  All  Sources,  Inter- 
agency Coordination."  1!)77.  pp.  10—11. 

•>  For  analysis  of  these  and  other  related  bills  concerned  with  Federal  organization  for 
weather  modification  see  Johnson.  Ralph  W..  "Federal  Organization  for  Control  of  Weather 
Modification."  In  Howard  J.  Taubenfeld  (editor),  "Controlling  the  Weather,"  New  York. 
Dunellen.  1970.  pp.  145-158. 

64  Grant.  Lewis  (>..  testimony  in  :  U.S.  Congress,  House  of  Representatives,  Committee  on 
Science  and  Technology,  Subcommittee  on  the  Environment  and  the  Atmosphere.  "Weather 
Modification."  hearings,  04th  Cong..  2d  sees.,  June  15-18,  1977.  Washington,  D.C..  U.S. 
Government  Frinting  Office,  1976,  p.  290. 


sion  users.  Present  fragmentation  of  effort,  combined  with  subcritical  support 
levels,  retards  adequate  progress  toward  the  goal  of  problem  resolution  and  de- 
velopment of  application  capability. 

I  suggest  that  a  commission-type  approach  be  considered.  This  would  permit 
representation  of  various  weather  modification  missions  by  researchers,  users, 
and  the  general  public.  Such  a  commission  could  develop  a  comprehensive  and 
coordinated  national  weather  modification  policy  and  program  of  weather  modi- 
fication research.  ...  A  positive  national  program  and  funding  levels  could  be 
recommended  to  Congress.  I  believe  that  management  of  the  program  through 
this  commission  for  the  next  five  to  ten  years  should  also  be  considered.  The 
highest  standards  possible  and  the  broadest  representation  possible  should  be 
required  for  this  commission  and  its  staff. 

As  the  technological  capability  develops  and  can  respond  to  various  uses,  the 
lull  responsibility  for  the  respective  uses  could  transfer  to  the  mission  agencies 
at  that  time.  Continued  involvement  by  the  agencies  during  the  development 
stages  could  make  a  smooth  transition  possible.  If  the  national  research  and 
development  program  is  organized  and  managed  through  such  a  commission,  the 
commission  should  not  have  the  dual  role  of  regulating  weather  modification  at 
the  same  time  it  has  the  responsibility  for  its  developmient.85 

Changnon  has  recommended  an  almost  total  reorganization  of  the 
Federal  weather  modification  structure  in  order  to  handle  better  the 
current  major  research  responsibilities;  evaluation  efforts  needed  im- 
mediately, which  are  not  being  addressed ;  and  readiness  to  perform  re- 
sponsibilities of  the  near  future,  including  operations,  regulation,  and 
compensation.  He  suggests  twro  approaches  to  this  reorganization, 
shown  schematically  in  figure  l.66 

In  his  first  approach,  Changnon  would  place  all  weather  modifica- 
tion activities,  except  regulation  and  compensation,  in  one  agency 
(Agency  X,  fig.  la),  either  a  new  agency  or  a  division  of  one  exist- 
ing. From  a  weather  modification  and  a  user  standpoint  the  likely  can- 
didates proposed  among  existing  agencies  are  the  U.S.  Department  of 
Agriculture  and  XOAA.  This  primary  agency  would  develop  a  na- 
tional laboratory  which  would  both  conduct  research  and  development 
and  also  subcontract  such  efforts.  The  agency  and  its  laboratory  would 
be  responsible  for  program  design,  monitoring,  and  evaluation  of  all 
experimental  and  operational  projects  and  would  report  results  to  the 
regulatory  agency  (Agency  Y,  fig.  la).  The  laboratory  would  also 
be  responsible  for  Federal  operational  efforts  and  for  development  of 
guidelines  for  private  operators.  Close  interaction  would  be  required 
with  the  States,  private  business,  and  the  public  within  operational 
regions.  Agency  Y  could  be  a  new  agency  or  an  existing  one,  such  as 
the  Environmental  Protection  Agency  or  XOAA.  provided  that  NOAA 
is  not  also  chosen  as  Agency  X.  Agency  Y  would  also  develop  and  ad- 
minister compensatory  mechanisms  to  benefit  those  identified  as  losers 
as  a  result  of  weather  modification  programs.  This  first  approach  would 
also  include  a  Presidential  board  or  commission  of  appointed  non- 
Federal  members  with  statutory  responsibility  for  reporting  annually 
to  the  President  and  the  Congress  on  all  weather  modification  activi- 
ties performed  by  Agencies  X  and  Y.67 

05  Ibid.,  pp.  290-291. 

66  Changnon.  Stanley  A..  Jr..  "The  Federal  Role  in  Weather  Modification."  background 
paper  prepared  for  the  U.S.  Department  of  Commerce  Weather  Modification  Advisory 
Board.  Urbana.  111.,  Mar.  9.  1977,  pp.  24-27. 

87  Ibid.,  pp.  25-26. 



In  Changnon's  second  organizational  approach,  there  are  similarities 
to  the  first,  but  current  research  activities  would  be  retained  with  some 
Federal  agencies  (see  fig.  lb).  Agency  Y  would  handle  regulatory- 
compensatory  functions  as  in  the  first  approach,  and  a  Presidential 
board  or  commission  would  make  critical  annual  assessments  of  the 
progress  and  activities  in  all  agencies  as  well  as  report  annually  to  the 
President  and  the  Congress.  A  major  agency,  new  or  existing,  would 
have  direct  responsibility  for  its  own  activities  as  well  as  the  research 
programs  of  other  Federal  agencies.  Thus,  existing  programs  of  the 
Departments  of  Agriculture,  Commerce,  and  Defense  and  of  the  Na- 
tional Science  Foundation  would  continue,  but  under  direction  of 
Agency  X,  each  program  directed  toward  specific  agency  missions. 
Other  agencies  currently  involved  in  weather  modification — the  De- 
partments of  Energy,  Interior,  and  Transportation,  and  the  National 
Aeronautics  and  Space  Administration — would  be  stripped  of  their 

In  his  1970  paper,  Johnson  explored  some  of  the  more  plausible  in- 
stitutional arrangements  that  could  be  designed  for  Federal  manage- 
ment of  weather  modification.69  He  identified  the  various  functions 
into  which  such  management  responsibilities  could  be  divided  and  at- 
tempted to  show  the  optimum  ways  that  each  function  might  be 
handled.  A  major  point  which  Jolmson  made  then,  which  is  still  ap- 
propriate today,  is  that  the  Federal  institutional  arrangements  should 
depend  on  the  pace  of  the  development  of  weather  modification  tech- 
nology. Thus,  establishment  of  a  full-blown  structure  dealing  with  all 
weather  modification  functions  may  not  yet  be  advisable,  even  in  1973. 



There  are  a  number  of  formal  and  informal  mechanisms  by  which 
the  Federal  research  program  in  weather  modification  is  coordinated, 
and  there  exist  a  variety  of  panels,  committees,  and  organizations — 
some  governmental  and  some  quasi-governmental — which  provide  ad- 
vice and  a  forum  for  exchange  of  information  on  various  aspects  of 
weather  modification.  Coordination  is  also  achieved  through  profes- 
sional society  meetings  and  through  workshops  on  specific  problems 
which  are  scheduled  by  Federal  agencies  from  time  to  time. 

Much  of  the  coordination  of  weather  modification  projects  attempted 
by  agency  representatives  consists  of  exchange  of  information  on  the 
scope  and  the  funding  of  the  different  agency  programs,  this  ex- 
change accomplished  through  meetings  of  committees,  conferences, 
and  panels.  Through  such  exchange  it  is  expected  that  consensus  can 
be  approached  and  coordination  achieved. 

Various  opinions  have  been  expressed  on  the  degree  to  which  Fed- 
eral weather  modification  programs  are  coordinated.  According  to 
Droessler,  "The  weather  modification  research  program  probably  is 
as  well  coordinated  as  any  research  effort  within  the  Federal  Govern- 

68  Ibid.,  p.  26-27. 

89  Johnson,  "Federal  Organization  or  Control  of  Weather  Modification,"  1970,  pp.  131-1S0. 

34-SoT— 79  17 


ment."  70  Dr.  Alfred  J.  Eggers,  Jr.,  former  Assistant  Director  for  Re- 
search Applications  at  the  S"SF  has  recently  stated  that : 

In  summary,  the  current  programs  in  weather  modification  of  the  various 
agencies  appear  to  be  sufficiently  well  coordinated  to  avoid  unknowing  duplica- 
tions of  efforts,  but  not  so  rigidly  coordinated  as  to  unduly  narrow  the  range 
of  scientific  approaches  being  taken  to  respond  to  several  agency  missions. 
Weather  modification  is  not  a  well-developed  technology.  Given  the  current 
state  of  the  art,  the  current  mechanisms  of  coordination  appear  to  be  appropriate 
and  adequate.71 

A  contrary  view  was  stated  in  the  report  by  the  General  Accounting 
Office  (GAO)  on  the  need  for  a  national  program  in  weather  modifica- 
tion research : 

A  national  program  in  weather  modification  research  is  necessary  to  effectively 
control  activities  of  the  agencies  involved.  Although  this  need  was  recognized  as 
early  as  1966.  the  organizations  established  to  coordinate  these  activities  have 
not  developed  and  implemented  an  effective  overall  national  program.  Although 
coordinating  groups  have  tried  to  develop  national  programs,  their  implementa- 
tion has  not  been  successful.  The  present  fragmentation  of  research  efforts  has 
made  it  extremely  difficult  for  agencies  to  conduct  effective  field  research  which, 
in  the  case  of  weather  modification,  must  precede  operational  activities.72 

In  answer  to  this  conclusion  of  the  GAO  report  that  the  Federal 
weather  modification  research  program  was  not  effectively  coordi- 
nated, the  Office  of  Management  and  Budget  (OMB)  replied  that: 

The  point  on  ineffective  coordination  of  research  projects  is  not  supported  by 
fact.  Weather  modification  research  is  well  coordinated  by  the  Interdepartmen- 
tal Committee  on  Atmospheric  Sciences  (ICAS).  ICAS  meets  monthly  and  pro- 
vides members  and  observers  the  opportunity  to  exchange  information  in  a  timely 
manner.  Interdepartmental  coordination  of  weather  modification  activities  has 
been,  in  our  opinion,  achieved  through  the  efforts  of  ICAS  and  the  member 
agencies  in  an  exemplary  manner.7'' 

The  several  means,  formal  and  informal,  by  which  the  Federal 
weather  modification  research  program  is  coordinated,  or  by  which 
advice  on  agency  programs  is  provided,  are  identified  and  discussed  in 
the  following  subsections. 

The  Interdepartmental  Committee  for  Atmospheric  Sciences  (ICAS) 

The  principal  mechanism  for  coordination  of  Federal  weather 
modification  programs  has  been  the  ICAS.  Weather  modification 
has  been  a  principal  concern  of  the  committee  since  its  inception  in 
1959,  and  it  was  recently  stated  that  the  ICAS  has  spent  more  effort 
dealing  with  weather  modification  than  with  any  other  single  topic.74 
This  close  tie  and  continued  interest  by  the  ICAS  on  weather  modi- 
fication was  instilled  from  its  beginning,  when  it  incorporated  func- 
tions of  an  existing  interagency  weather  modification  committee. 

In  195s.  the  National  Science  Foundation  recognized  the  need  for 
a  formal  interagency  coordinating  mechanism  as  part  of  its  newly 

70  Droessler.  "Weather  Modification  :  Federal  Policies,  Funding  From  All  Sources,  Inter- 
agency Coordination,"  1!*77.  p.  14. 

71  Eggers,  testimony  before  House  Committee  on  Science  and  Technology,  Subcommittee 
on  the  Environment  and  the  Atmosphere.  107(5.  pp.  111-112. 

-  Comptroller  of  the  United  States.  "Need  for  a  National  Weather  Modification  Research 
Propnim  '*  report  to  the  Congress,  General  Accounting  Office,  B-133202,  Washington,  D.C., 
Aug.  23.  1974,  p.  23. 

Sawhlll.  John  C.  Associate  Director,  Office  of  Management  and  Budget.  In  a  letter  to 
Morton  B.  Henig,  Associate  Director,  Manpower  and  Welfare  Division,  General  Accounting 
Office.  Sept.  12.  1973. 

74  Todd.  Edward  P.  (Chairman  of  the  Tn t erdepartmental  Committee  for  Atmospheric  Sci- 
ences), in  testimony  at  hearings  on  weather  modification  before  the  Subcommittee  on  the 
Environment  and  the  Atmosphere.  Committee  on  Science  and  Technologv.  U  S.  House  of 
Representatives,  June  16,  1976,  p.  127. 


assigned  statutory  responsibilities  as  weather  modification  lead  agency 
and  established  an  Interdepartmental  Committee  on  Weather  Modi- 
fication. A  year  later  the  newly  established  Federal  Council  for  Sci- 
ence and  Technology  (FCST)  considered  the  need  for  a  committee  to 
cover  atmospheric  sciences;  and,  upon  agreement  between  the  Presi- 
dent's science  adviser  and  the  Director  of  the  XSF,  the  existing  Inter- 
departmental Committee  on  Weather  Modification  was  formally 
reconstituted  as  the  FCST's  Interdepartmental  Committee  for  At- 
mospheric Sciences.  ICAS  held  its  first  meeting  September  9,  1959. 75> 76 

The  National  Science  and  Technology  Policy,  Organization,  and 
Priorities  Act  of  1976  (Public  Law  94-282)  was^  signed  May  11,  1976, 
creating  the  Federal  Coordinating  Council  for  Science,  Engineering, 
and  Technology  (FCCSET) .  Under  the  new  law,  the  ICAS,  a  subcom- 
mittee of  the  former  FCST.  should  have  ceased  to  function,  since 
the  parent  council  was  abolished.  Prior  to  the  signing  of  Public  Law 
94-282,  however,  the  FCST  Chairman  addressed  a  letter  to  all  FCST 
subcommittee  chairmen,  indicating  that  these  committees  should  con- 
tinue their  normal  activities  until  such  time  as  a  new  organizational 
structure  for  FCCSET  could  be  established  and  begin  to  function. 
Subsequently,  the  FCCSET  established  several  supporting  subcom- 
mittees, one  of  which  is  the  Committee  on  Oceans  and  Atmosphere 
(CAO) .  The  ICAS  was  formally  adopted  by  the  CAO  on  a  temporary 
basis,  pending  creation  of  its  own  subcommittee  structure.  Conse- 
quently, the  ICAS  lias  continued  to  hold  meetings  and  published  its 
customary  annual  report,  under  authority  given  by  the  Chairman  of 
the  CAO.77  Although  the  future  of  the  ICAS  is  uncertain,  a  recent 
survey  indicated  that  its  members  favored  continuation  of  an  *'ICAS- 
like'?  activity.  The  committee  thus  intends  to  meet  and  conduct  business, 
at  a  reduced  level  of  activity,  until  the  CAO  organization  becomes  firm 
and  is  in  full  operation.78 

The  coordination  activities  of  the  ICAS  for  the  Federal  weather 
modification  research  program  has  been  particularly  valuable,  espe- 
cially since  1968,  when  the  Xational  Science  Foundation  was  relieved 
of  its  lead  agency  role.  Prior  to  that  time  the  XSF  had  provided  leader- 
ship to  the  Federal  program  in  a  number  of  ways.  Beginning  in  1969 
the  ICAS  has  continued  the  sponsorship  of  the  annual  Interagency 
Conference  on  Weather  Modification,  which  the  XSF  had  initiated  10 
years  earlier.  This  annual  conference  is  a  "partial  mechanism  to  pro- 
mote effective  communications  and  a  source  of  shared  responsibility 
among  the  Washington  program  managers  and  the  field  program 
managers."  79  These  conferences  provide  a  forum  for  exchanging  in- 

75  Special  Commission  on  Weather  Modification.  '"Weather  and  Climate  Modification,"  re- 
port to  the  National  Science  Foundation.  XSF  66-3,  Washington.  D.C..  Dec.  20.  1965,  p.  131. 

76  A  discussion  of  the  history  and  activities  of  the  Federal  Council  for  Science  and  Tech- 
nology is  found  in  the  following  report:  Bates.  Dorothy  M.  (coordinator).  Interagency  Co- 
ordination of  Federal  Scientific  Research  and  Development  :  The  Federal  Council  for  Sci- 
ence and  Technology.  Report  prepared  by  the  Science  Policy  Research  Division  of  the  Con- 
gressional Research  Service  for  the  Subcommittee  on  Domestic  and  International  Scientific 
Planning  and  Analysis.  Committee  on  Science  and  Technology.  U.S.  House  of  Representa- 
tives. Committee  Print.  Washington.  U.S.  Government  Printing  Office,  1976.  447  pp.  Of  spe- 
cial interest  in  this  report  is  a  case  history  of  the  ICAS:  Morrison.  Robert  E.  The  Inter- 
departmental Committee  for  Atmospheric  Sciences  :  a  case  history.  App.  Ln  pp.  381-396. 
(Included  in  the  case  history  is  a  list  of  ICAS  publications  through  July  1976.) 

"  Federal  Coordinating  Council  for  Science.  Engineering,  and  Technology.  Committee  on 
Oceans  and  Atmosphere.  Interdepartmental  Committee  for  Atmospheric  Sciences.  National 
Atmospheric  Sciences  Program  :  fiscal  year  1978.  ICAS  21-FY7S.  September  1977,  96  pp. 

7S  Ibid.,  p.  iii. 

"9  Drossier.  Weather  Modification:  Federal  Policies.  Funding  From  All  Sources  Inter- 
agency Coordination,  p.  14. 


formation  on  progress  in  past  years,  plans  for  the  coming  year, 
thoughts  on  future  projects,  and  suggestions  on  solutions  to  various 
problems  encountered.  The  annual  conferences,  under  ICAS  sponsor- 
ship, beginning  with  the  11th  in  1969,  have  been  hosted,  at  the  request 
of  the  ICAS,  by  the  NSF  and  by  NOAA.  The  NSF  hosted  the  11th 
conference,  and  XOAA  has  hosted  all  of  those  since,  starting  with 
the  12th. 

At  regular  meetings  of  the  ICAS,  major  weather  modification  pro- 
grams of  member  agencies  are  frequently  reviewed  through  project 
briefings  by  Washington  and  field  program  managers.  The  ICAS  has 
formed  standing  and  ad  hoc  panels  to  which  are  assigned  responsibili- 
ties for  specific  facets  of  the  weather  modificaion  program.  Panels  in 
the  past  have  worked  on  problems  such  as  legislation  on  weather  modi- 
fication, a  national  plan  for  the  Federal  weather  modification  program, 
and  a  plan  for  accelerating  progress  in  weather  modification.  These 
panels  address  topics  as  requested  by  the  parent  committee  and  make 
recommendations  to  the  ICAS  for  actions  as  required.  Two  specific 
ICAS  reports  have  dealt  with  the  subject.80'  81 

Besides  formal  coordination  afforded  by  the  annual  conferences,  dis- 
cussions at  ICAS  meetings,  and  studies  undertaken  by  ICAS  panels, 
there  is  also  included  an  account  of  the  Federal  weather  modification 
program  as  an  appendix  to  the  annual  ICAS  report.82  In  the  early 
years  of  the  ICAS  member  agencies  reported  their  funding  for  the 
general  support  of  atmospheric  sciences  only  in  two  broad  categories, 
meteorology  and  aeronomy.  Beginning  with  fiscal  year  1963  the  agen- 
cies began  to  identify  specific  funds  for  weather  modification,  and  this 
information  has  been  included  since  in  the  annual  ICAS  report  along 
with  brief  descriptions  of  member  agency  programs. 

It  was  at  the  request  of  the  ICAS  and  with  the  cooperation  of  the 
Secretary  of  Commerce  that  Federal  agencies  began  to  report  their 
weather  modification  research  activities  to  XOAA  as  of  November  1, 
1973.83  Public  Law  92-205  requires  such  reporting  by  all  nonfederal!}' 
sponsored  weather  modification  projects  in  the  United  States  and  its 
territories.84  This  voluntary  reporting  by  Federal  agencies,  initiated 
by  the  ICAS,  thus  assured  that  the  central  source  of  information  on 
weather  modification  projects  in  the  United  States  is  reasonably 

In  its  1971  annual  report,  the  ICAS  identified  selected  major  re- 
search projects  in  weather  modification  which  were  designated  as  na- 
tional projects.85  These  national  projects  were  formulated  by  the 
ICAS  members  through  combination  of  agency  projects  in  each  of 
seven  categories  of  weather  modification  assigning  lead  agency  respon- 
sibilities in  most  cases  to  that  agency  with  the  most  significant  ongoing 

80  Newell.  Homer  E.  A  recommended  national  program  in  weather  modification.  Federal 
Council  for  Science  and  Technology.  Interdepartmental  Committee  for  Atmospheric  Sci- 
ences ICAS  report  No.  10a.  Washington.  D.C.,  November  1966.  93  pp. 

81  Federal  Council  for  Science  and  Technology.  Interdepartmental  Committee  for  Atmos- 
pheric Sciences.  ICAS  report  No.  15a.  Washington.  D.C.,  June  1971,  50  pp. 

82  The  most  recent  account  is  found  in  the  latest  ICAS  annual  report :  Federal  Coordinat- 
ing Council  for  Science.  Engineering,  and  Technology.  Interdepartmental  Committee  for 
Atmospheric  Sciences.  ICAS  21-FY7S.  Pp.  87-94. 

83  Federal  Council  for  Science  and  Technology.  Interdepartmental  Committee  for  Atmos- 
pheric Sciences.  National  Atmospheric  Sciences  Program  :  fiscal  rear  1975.  ICAS  18-FY  75 
Washington,  DC.  May  1974.  n.  iv. 

M  See  earlier  discussions  on  Public  Law  92  205  under  congressional  activities,  p.  197.  and 
under  tbe  administration  of  the  reporting  program  by  NOAA.  p.  2'.V2. 

Federal  Council  for  Science  and  Technology.  Interdepartmental  Committee  for  Atmos- 
pheric Sciences.  National  Atmospheric  Sciences  Program  :  fiscal  year  1972.  ICAS  report 
No.  15.  March  1971,  pp.  5-6. 


project (s)  within  each  category.  The  proposed  national  projects  and 
respective  lead  agencies  were : 

1.  National  Colorado  River  Basin  pilot  project. — Bureau  of  Recla- 
mation, Department  of  the  Interior :  To  test  the  feasibility  of  apply- 
ing a  cloud  seeding  technology,  proven  effective  under  certain  condi- 
tions, to  a  river  basin  for  a  winter  season  to  augment  the  seasonal 

'2.  National  hurricane  modification  project. — National  Oceanic  and 
Atmospheric  Administration,  Department  of  Commerce :  To  develop 
a  seeding  technology  and  associated  mathematical  models  to  reduce 
the  maximum  surface  winds  associated  with  hurricanes. 

3.  National  lightning  suppression  project. — Forest  Service,  Depart- 
ment of  Agriculture :  To  develop  a  seeding  technology  and  associated 
physical  and  mathematical  models  to  reduce  the  frequency  of  forest 
fire-starting  lightning  strokes  from  cumulonimbus  clouds. 

4.  National  cumulus  modification  project. — National  Oceanic  and 
Atmospheric  Administration,  Department  of  Commerce :  To  develop 
a  seeding  technology  and  associated  mathematical  models  to  promote 
the  growth  of  cumulus  clouds  in  order  to  increase  the  resulting  natural 
rainfall  in  areas  where  needed. 

5.  National  hail  research  experiment. — National  Science  Founda- 
tion :  To  develop  a  seeding  technology  and  associated  mathematical 
models  to  reduce  the  incidence  of  damaging  hailfall  from  cumulonim- 
bus clouds  without  adversely  affecting  the  associated  rainfall. 

6.  National  Great  Lakes  snoio  redistribution  project. — National 
Oceanic  and  Atmospheric  Administration,  Department  of  Commerce  : 
To  develop  a  seeding  technology  and  associated  mathematical  models 
to  spread  the  heavy  snowfall  of  the  Great  Lakes  coastal  region  farther 

7.  National  fog  modification  project. — Federal  Aviation  Adminis- 
tration, Department  of  Transportation :  To  develop  seeding  or  other 
technology  and  associated  physical  and  mathematical  models  to  reduce 
the  visibility  restrictions  imposed  by  warm  and  cold  fogs  where  and  to 
the  extent  needed.86 

Although  most  of  these  national  projects  were  continued  for  at  least 
a  while,  some  of  them  failed  to  materialize,  as  hoped,  as  truly  national 
projects.  Few  received  the  expected  interagency  support  and  planning 
effort  envisioned;  however,  in  spite  of  these  deficiencies,  some  were 
pursued  by  the  lead  agencies,  largely  as  major  single-agency  projects. 
The  National  Hail  Research  Experiment,  conducted  by  the  National 
Science  Foundation  perhaps  came  closest  to  a  truly  national  project 
and.  with  assistance  from  other  Federal  agencies,  continued  through 
1976. 87  A  critique  of  the  national  projects  in  weather  modification  was 
included  in  the  1974  report  of  the  General  Accounting  Office  on  the 
need  for  a  national  program  in  weather  modification  research.88 

In  answer  to  charges  that  the  Federal  weather  modification  research 
effort  has  been  poorly  coordinated,  a  conclusion  of  various  studies  that 
have  been  made,  the  Chairman  of  the  ICAS  recently  said,  "Within  the 
IOAS  we  have  considered  coordination  as  it  is  defined,  namely,  har- 

»  Ibid. 

Shc  discussion  of  the  national  bail  research  project  under  following  section  on  the  pro- 
gram of  the  National  Science  Foundation,  p.  274  ff. 

^Comptroller  General  of  the  United  States.  Need  for  a  national  weather  modification 
research  program.  B-133202,  1974.  Pp.  16-22. 


monious  action,  communication  within  Government.  I  submit  that,, 
using  that  definition,  the  weather  modification  research  program  is 
probably  as  well  coordinated  as  any  effort  within  the  Government,  with 
the  possible  exception  of  programs  that  are  entirely  within  the  purview 
of  a  single  agency.  The  critics  of  the  ICAS  coordination  effort,  how- 
ever, seem  to  nave  been  interpreting  coordination  as  including  manage- 
ment ;  the  ICAS  is  not  a  management  agent.'' 89 

The  National  Academy  of  Sciences/ Committee  on  Atmospheric  Sci- 
ences (N AS/GAS) 

Advice  has  been  provided  to  the  Federal  Government  through  ad- 
visory panels,  intensive  studies,  and  published  reports  on  weather 
modification,  by  the  National  Academy  of  Sciences.  The  Committee 
on  Atmospheric  Sciences  (CAS)  was  organized  under  the  National 
Research  Council  of  the  Academy  in  1956,  with  the  stated  purpose  of 
addressing  .  .  itself  to  the  task  of  viewing  in  broad  perspective  the 
present  activities  in  research  and  education,  the  exchange  of  informa- 
tion and  related  matters  as  they  affect  the  status  of  the  field  and  future 
progress  toward  a  balanced  national  program  in  the  atmospheric 
sciences,  and  participation  in  international  programs."  90 

At  the  request  of,  and  sponsored  by,  the  National  Science  Founda- 
tion, a  conference  was  organized  and  conducted  by  the  NAS  in  1959, 
in  which  meteorologists,  mathematicians,  and  statisticians  met  to  ex- 
amine needs  in  weather  modification  experiments.  The  report  on  this 
Skyline  Conference  on  the  Design  and  Conduct  of  Experiments  in 
Weather  Modification,91  which  had  been  held  in  the  Shenandoah  Na- 
tional Park  in  Virginia,  made  a  strong  plea  for  careful  statistical 
design  of  weather  modification  experiments,  pointing  out  the  need  for 
long-term  programs,  standardization  of  design,  the  need  for  basic 
research  in  cloud  physics,  and  the  requirement  for  cooperation  between 
meteorologists  and  statisticians. 

In  March  1963,  the  CAS  appointed  a  Panel  on  Weather  and  Climate 
Modification,  "to  undertake  a  deliberate  and  thoughtful  review  of  the 
present  status  and  activities  in  this  field  and  of  its  potential  and  limi- 
tations in  the  future."  92  The  Panel  was  chaired  by  Dr.  Gordon  J.  F. 
MacDonald  and  was  comprised  of  11  Government  and  non-Govern- 
ment members.  The  Academy  Panel  worked  closely  with  the  NSF's 
Special  Commission  on  Weather  Modification,  which  had  been  estab- 
Lished  in  1964.  Three  reports  were  subsequently  published  by  the  Panel,, 
based  on  in-depth  studies  which  had  been  undertaken. 

The  first  of  these,  "Scientific  Problems  of  Weather  Modification," 
appeared  in  1964;  03  the  second,  "Weather  and  Climate  Modification: 
Problems  and  Prospects,"  was  published  in  1966; 94  and  the  third, 

89  Todd.  Testimony  before  House  Committee  on  Science  and  Technology,  Subcommittee  on 
the  Environment  and  the  Atmosphere.  June  197fi.  p.  S7. 

90  National  Academy  of  Sciences,  National  Academy  of  Engineering.  Institute  of  Medicine; 
National  Research  Council.  Organization  and  members:  1975-1976.  Washington,  D.C.  Octo- 
ber 1975.  P.  81. 

n  National  Academy  of  Sciences.  National  Research  Council.  Report  of  the  Skyline  Con- 
ference on  the  Design  ami  Conduct  of  Experiments  in  Weather  Modification.  NAS— NBC  Pub- 
lication 742.  Washington.  D.C,  l!tn').  24  pp. 

92  National  Academy  of  Sciences.  National  Research  Council.  Committee  on  Atmospheric 
Sciences.  Weather  and  Climate  Modification:  Problems  and  Prospects.  Volume  I.  summary 
and  recommendations.  Final  report  of  the  Panel  on  Weather  and  Climate  Modification.  Pub- 
lication No.  1350,  Washington,  D.C,  I960,  p.  vii. 

m  National  Academy  of  Sciences.  National  Research  Council.  Committee  on  Atmospheric 
Sciences  Scientific  Problems  of  Weather  Modification  :  a  Report  of  the  Panel  on  Weather 
and  Climate  Modification.  NAS  NRC  Publication  No.  1236.  Washington.  D.C.  1964.  56  pp. 

ot  National  Academy  of  Sciences.  Publication  No.  1350.  1906.  In  two  volumes.  40  +  212  pp. 


"Weather  Modification :  Problems  and  Progress,"  came  out  in  1973.95 
In  addition  to  the  reports  produced  by  the  panel,  two  other  National 
Academy  studies  were  conducted  in  the  1970's  which,  in  part,  addressed 
aspects  of  weather  modification.  The  Committee  on  Atmospheric  Sci- 
ences surveyed  the  field  in  a  chapter  in  its  1971  publication,  "The 
Atmospheric  Sciences  and  Man's  Needs ;  Priorities  for  the  Future."  96 
In  1976  a  report  was  prepared  by  the  Committee  on  Climate  and 
Weather  Fluctuations  and  Agricultural  Production  of  the  Board  on 
Agriculture  and  Eenewable  Resources.  A  full  chapter  is  devoted  to 
weather  modification  in  this  report,  entitled  "Climate  and  Food; 
Climatic  Fluctuation  and  U.S.  Agricultural  Production." 97 

Project  Stormfury,  a  major  hurricane  modification  project  of  the 
Commerce  Department's  National  Oceanic  and  Atmospheric  Admin- 
istration (NO  A  A), 98  from  its  inception  has  had  an  advisory  panel 
composed  of  prominent  scientists,  primarily  meteorologists.  Currently, 
the  panel  is  appointed  by  and  operates  under  the  auspices  of  the  Na- 
tional Academy  of  Sciences,  Committee  on  Atmospheric  Sciences. 
Members  of  the  Stomfurv  Advisory  Panel  all  come  from  either  the 
academic  community  or  from  private  industry.  Not  only  does  the  Panel 
review  program  results  and  experimental  designs  and  make  recom- 
mendations, but  it  also  conducts  periodic  scientific  symposia  before 
larger  groups.  A  recent  program  review  was  held  in  September  1977, 
and  a  report  on  the  review  is  in  preparation. 

The  National  Advisory  Committee  on  Oceans  and  Atmosphere 

This  advisory  committee  was  created  by  Public  Law  92-125  on 
August  16, 1971,  and  was  to  be  advisory  to  both  the  President  and  the 
Congress  on  the  Nation's  atmospheric  and  marine  affairs  and  to  the 
Secretary  of  Commerce  with  respect  to  the  programs  of  the  National 
Oceanic  and  Atmospheric  Administration  (NOAA).  Among  other 
duties,  the  committee  was  charged  with  assessing  the  status  of  U.S. 
atmospheric  and  oceanic  activities  and  with  submitting  an  annual  re- 
port of  its  findings  and  recommendations  to  the  President  and  the 
Congress.  The  Secretary  of  Commerce  was  also  required,  on  behalf  of 
the  executive  branch,  to  prepare  comments  on  the  NACOA  recom- 
mendations. These  comments  are  appended  to  each  of  the  annual 
NACOA  reports. 

As  originally  constituted  by  Public  Law  95-125,  NACOA  included 
25  members,  all  non-Federal,  appointed  by  the  President,  who  also' 
designated  one  of  the  members  as  chairman  and  one  as  vice  chairman. 
Each  department  and  agency  of  the  Federal  Government  concerned 
with  atmospheric  and  marine  matters  was  to  designate  a  senior  policy 
official  to  participate  as  observer  and  to  offer  assistance  as  required. 
The  Secretary  of  Commerce  was  to  make  available  such  staff,  person  - 

95  National  Academy  of  Sciences.  National  Research  Council.  Committee  on  Atmospheric 
Science^  Weather  Modification  :  Problems  and  Progress.  ISBN  0-309-02121-9.  Washing- 
ton, D.C.,  1973.  280  pp. 

98  National  Academy  of  Sciences.  National  Research  Council.  Committee  on  Atmospheric 
£c.V^ce^T£e.Atmospheric  Sciences  and  Man's  Needs;  Priorities  for  the  Future.  ISBN 
0-300-01912-5.  Washington,  D.C.,  May  1971,  pp.  42-61. 

97  National  Academy  of  Sciences.  National  Research  Council.  Board  on  Agriculture  and 
Renewable  Resources.  Climate  and  Food  ;  Climatic  Fluctuation  and  U.S.  Agricultural  Pro- 
duction. ISBN  O-309-02522-2.  Washington,  D.C..  1976  pp.  131-162 

ps  For  discussion  of  Project  Stormfury,  see  p.  296  under  weather  modification  pro-rams 
Of  the  Department  of  Commerce. 


nel,  information,  and  administrative  services  as  reasonably  required 
to  carry  out  committee  activities.  The  life  of  NACOA  was  extended 
and  its  appropriation  authorization  was  increased  successively  by 
Public  Laws  92-657  and  94-69  of  October  25,  1972,  and  August  16, 
1975,  respectively.  The  1971  act  was  repealed,  however,  by  Public  Law 
95-63,  of  July  5,  1977,  which  effectively  disbanded  the  previous  com- 
mittee and  established  a  new  NACOA.  Although  many  of  the  provi- 
sions of  the  new  law  were  similar  to  the  previous  one,  the  size  of  the 
committee  was  reduced  from  25  to  18  members,  appointed  by  the 
President  .with  the  stipulation  that  members  must  be  eminently  quali- 
fied in  knowledge  and  expertise  in  areas  of  direct  concern  to  the  com- 
mittee, that  is,  in  atmospheric-  and  marine-oriented  disciplines. 

Since  its  inception,  the  posture  of  NACOA  has  been  to  concentrate 
its  studies  on  those  important  issues  where  it  can  make  a  significant 
contribution,  recognizing  that  an  attempt  to  review  and  evaluate  every 
program  and  issue  within  its  purview  of  responsibility  could  result 
in  treating  none  of  them  well  and  could  possibly  duplicate  what  others 
are  capable  of  doing  better."  Among  other  important  topics,  weather 
modification  has  been  the  subject  of  examination,  deliberation,  and 
comment  often  throughout  the  6  years  of  NACOA's  existence. 

Each  of  the  six  NACOA  annual  reports  have  contained  discussion 
and  recommendations  on  weather  modification,  which  was  one  of  the 
four  major  topics  covered  extensively  in  the  first  annual  report.1 
NACOA's  repeated  position  has  been  that  there  is  a  need  for  "a  coordi- 
nated Federal  effort  to  support  the  basic  research  needed  to  bring 
weather  modification  to  the  point  of  being  an  operational  tool  resting 
on  a  sound  technical  base"  but  that  "major  gaps  remain,  largely  be- 
cause no  one  agency  has  the  responsibility  for  identifying  and  support- 
ing those  areas  of  basic  study  needed  for  further  progress  along  a 
broad  front."  2  Specific  recommendations  of  NACOA  on  the  Federal 
weather  modification  program  will  be  discussed  in  the  following  chap- 
ter of  this  report  on  studies  and  recommendations.3 

Other  coordination  and  advisory  mechanisms 

Although  overall  coordination  of  the  Federal  weather  modification 
programs  has  been  an  ICAS  responsibility,  there  are  other  panels 
which  assist  certain  agencies  in  connection  with  major  research  proj- 
ects, and  there  have  been  various  workshops  on  particular  problem 
areas  through  which  interagency  consensus  has  been  achieved.  The 
NSF  Weather  Modification  Advisory  Panel  has  provided  important 
guidance  to  the  weather  modification  research  activities  of  the  NSF. 
The  presence  of  representatives  from  both  the  Bureau  of  Reclamation 
and  NOAA,  the  other  agencies  with  major  weather  modification  pro- 
grams, was  designed  to  assure  a  high  level  of  coordination.  The 
National  Hail  Research  Experiment  (NHRE)  Advisory  Panel  of 
the  NSF  also  has  had  representatives  from  these  two  agencies. 
Research  proposals  received  by  the  NSF  are  reviewed  by  the  Bureau 

National  Advisory  Committee  on  Oceans  and  Atmosphere.  A  report  to  the  President  nnd 
the  Poncrres^.  First  annual  report.  June  30.  1972.  Washington,  D.C.,  U.S.  Government 
Printing  Office,  p.  iv. 
1  Ibid.,  pp.  19-29. 

:  National  Advisory  Committee  on  Oceans  nnd  Atmosphere,  a  report  to  the  President  and 
tt  <■  I  !ongre88.  sixth  annual  report.  June  30,  1977,  Washington,  D.C.,  U.S.  Government  Print- 

lng  Office,  p.  76. 
See  Ch.  6. 


of  Reclamation  and  by  NOAA,  thus  giving  a  direct  input  to  these 
agencies  in  the  decision  process  as  to  whether  individual  research  pro- 
posals are  to  be  funded  by  the  NSF.4 

The  agencies  coordinate  directly  with  each  other  at  the  working 
level  whenever  the  respective  programs  may  benefit  thereby.  A  close 
coordination  mechanism  was  established,  for  example,  between  the 
National  Hail  Research  Experiment  (NHRE)  of  the  NSF  and  the  Bu- 
reau of  Reclamation's  High  Plains  Cooperative  Program  (HIPLEX) , 
a  useful  and  practical  arrangement  in  view  of  the  geographical  prox- 
imity of  the  two  projects  in  northeastern  Colorado  and  northwestern 
Kansas,  respectively.5 

During  the  past  few  years  workshops  on  various  aspects  and  prob- 
lem areas  in  weather  modification  have  afforded  additional  oppor- 
tunity for  coordination.  In  1975  the  National  Science  Foundation  spon- 
sored a  symposium/workshop  on  the  suppression  of  hail  as  part  of  its 
National  Hail  Research  Experiment.6  The  NSF  also  sponsored  a  major 
workshop  on  inadvertent  weather  modification  at  Hartford,  Conn.,  in 
May  1977.7  Another  recent  workshop  sponsored  by  the  NSF  was 
held  in  August  1977  at  Fort  Collins.  Colo.,  on  extended  space  and  time 
effects  of  planned  weather  modification  activities.8 

Since  1967,  the  Bureau  of  Reclamation  has  conducted  nine  con- 
ferences as  part  of  its  "Project  Sky  water."  dealing  with  various  special 
topics  of  particular  concern  to  the  projects  and  to  planned  weather 
modification  in  general.  Some  of  these  Sky  water  conferences  have  been 
jointly  sponsored  with  other  agencies,  in  particular,  the  National 
Science  Foundation,  and  more  recent  conferences  have  been  conducted 
in  a  workshop  format.  Following  each  conference  proceedings  have 
been  published.  The  first  conference  was  held  at  Denver,  Colo.,  in  1967, 
on  the  subject  of  physics  and  chemistry  of  nucleation.9  The  most  recent 
conference  was  a  workshop,  held  in  November  1976,  at  Vail,  Colo., 
on  environmental  aspects  of  precipitation  management.10  One  day  of 
this  conference  was  sponsored  jointly  with  the  National  Science  Foun- 
dation. A  tenth  Skywater  Conference  is  a  workshop  scheduled  for 
June  1978,  at  Lake  Tahoe,  Calif.,  where  the  topic  will  be  the  Sierra 
Cooperative  Pilot  Project  of  Skywater.  This  conference  will  follow  a 
meeting  at  the  same  place,  sponsored  jointly  by  the  American  Meteoro- 
logical Society  and  the  Forest  Service  of  the  U.S.  Department  of  Agri- 
culture, on  Sierra  Nevada  mountain  meteorology. 

Also  of  interest  as  a  coordination  mechanism  was  the  November 
1975,  Special  Regional  Weather  Modification  Conference  on  Augmen- 

4  Eggers.  testimony  before  House  Committee  on  Science  and  Technology,  Subcommittee  on 
the  Environment  and  the  Atmosphere,  1976,  p.  110. 

5  Ibid.,  p.  111. 

6  National  Center  for  Atmospheric  Research,  NHRE  symposium/workshop  on  hail  and  its 
suppression,  working  group  reports.  Estes  Park.  Colo..  Sept.  21-28.  1976.  "National  Hail 
Research  Experiment."  technical  report  NCAR/7100-75/2,  November  1975,  130  pp. 

7  Robinson.  G.  D.  (Principal  Investigator),  inadvertent  weather  modification  workshop. 
May  23-27,  1977.  Hartford.  Conn.,  final  report  to  the  National  Science  Foundation,  under 
grant  No.  ENV-77-10186.  "Hartford,  the  Center  for  the  Environment  and  Man.  Inc.." 
November  1977.  CEM  Report  4215-604.  167  pp. 

s  Brown.  R>ith  J..  Robert  D.  Elliott,  and  Max  Edelstein  (editors).  "Transactions  of 
Workshop  on  Extended  Space  and  Time  Effects  of  Weather  Modification."  Aug.  8-12,  1977, 
Fort  Collins.  Colo.  Goleta,  Calif.,  North  American  weather  consultants,  February  1978 
(draft),  279  pp. 

9  U.S.  Department  of  the  Interior.  Bureau  of  Reclamation.  "Phvsics  and  Cbpmistrv  of 
Nucleation."  proceedings  ;  Skywater  Conference  I,  Denver.  Colo.,  July  10-12,  1967,  Denver. 
July  1967.  419  pp. 

10  U.S.  Department  of  the  Interior.  Bureau  of  Reclamation.  "Precipitation.  Man.  and  the 
Environment ;  an  Overview  of  Skywatpr  IX  Conference,"  second  week  of  November  1976, 
Vail,  Colo.,  Denver,  September  1977,  223  pp. 



tation  of  Winter  Orographic  Precipitation  in  the  Western  United 
States,  sponsored  jointly  by  the  American  Meteorological  Society,  the 
Department  of  Water  Resources  of  the  State  of  California,  the 
Weather  Modification  Association,  and  the  Bureau  of  Reclamation.11 

In  connection  with  Project  Sky  water,  the  Bureau  of  Reclamation 
has  established  a  number  of  advisory  boards  and  panels  from  time  to 
time  as  the  need  has  arisen.  These  groups  have  been  composed  of  both 
Government  and  non-Government  experts.  In  connection  with  the 
High  Plains  Cooperative  Project  (HIPLEX) ,  the  Bureau  of  Reclama- 
tion has  also  established  citizens*  panels  to  advise  on  local  problems; 
these  groups  have  included  local  government  officials  among  other  indi- 
viduals. Similar  local  advisory  groups  have  been  planned  for  the  Sierra 
Cooperative  Pilot  Project  and  are  now  being  organized. 

Another  means  of  coordination  is  provided  through  the  joint  spon- 
sorship of  some  Federal  research  efforts.  For  example,  the  weather 
modification  simulation  laboratory  at  the  Colorado  State  University, 
funded  through  the  National  Science  Foundation  by  three  Federal 
agencies,  is  a  facility  used  in  support  of  a  number  of  Federal  projects. 
The  National  Science  Foundation  has  funded  a  number  of  research 
studies  which  support  the  major  weather  modification  programs  of 
other  agencies,  particularly  those  of  the  Bureau  of  Reclamation  and 
the  National  Oceanic  and  Atmospheric  Administration. 

A  coordination  and  advisory  role  has  also  been  played  from  time  to 
time  by  the  committees  and  panels  which  have  been  established  to  con- 
duct major  weather  modification  policy  studies.  Notable  among  these 
groups  are  the  Advisory  Committee  on  Weather  Control,  established 
by  Congress  in  1953,  and  the  Weather  Modification  Advisory  Board, 
impaneled  by  the  Secretarv  of  Commerce  to  implement  requirements 
of  the  National  Weather  Modification  Policy  Act  of  1976.12 

Although  not  officially  sponsored  by  the  Federal  Government,  a 
forum  for  coordination  and  exchange  of  information  on  Federal  as 
well  as  non-Federal  programs  is  provided  through  the  meetings  and 
the  journals  of  professional  organizations.  The  American  Meteorologi- 
cal Society  (AMS)  has  sponsored  six  conferences  specifically  dealing 
with  weather  modification,  at  which  the  majority  of  the  papers  de- 
livered have  been  related  to  Federal  research  projects  and  at  which 
nearly  all  of  the  papers  have  been  based  on  federally  sponsored  re- 
search. Exchange  of  information  on  Federal  projects  has  also  been 
afforded  through  the  medium  of  AMS  journals,  particularly  the  "Bul- 
letin of  the  American  Meteorology  Society"  and  the  "Journal  of 
Applied  Meteorology."  Among  the  various  specialized  AMS  commit- 
tees is  the  Committee  on  Weather  Modification,  concerned  with  ad- 
vances and  priorities  in  weather  modification  research,  the  greatest 
portion  of  which  is  supported  in  the  United  States  by  the  Federal 
agencies.  In  addition,  specialized  conferences  on  some  problem  aspects 
of  weather  modification  have  been  sponsored  by  the  AMS,  sometimes 
jointly  with  various  Federal  agencies. 

"  American  Meteorological  Society,  Abstracts  of  Special  Regional  Weather  Modification 
Conference:  Augmentation  of  Winter  Orographic  Precipitation  in  the  Western  United 
States  Nov  11  13,  1975,  San  Francisco,  Calif.  (Cosponsored  by  the  U.S.  Department 
Of  the  Interior.  Bureau  of  Reclamation;  State  of  California,  Department  of  Water  Re- 
potirccs  ;  and  the  Weather  Modification  Association,  Boston  (no  publication  date),  24H  nn. 

12  The  purpose,  formation,  activities,  and  recommendations  of  these  committees  are  dis- 
eussed  in  some  detail  in  various  other  places  in  this  report. 


The  Weather  Modification  Association  (WMA)  sj^onsors  two  pro- 
fessional meetings  each  year,  sometimes  jointly  with  the  AMS  or  other 
professional  organizations,  and  also  published  the  "Journal  of 
Weather  Modification/'  These  WMA  mechanisms  provide  additional 
opportunities  for  coordination  of  Federal  projects  as  information  is 
exchanged  among  participants,  many  of  whom  are  employees  of  Fed- 
eral agencies  or  of  contractors  on  Federal  projects.  The  organization, 
purposes,  and  activities  of  the  AMS,  the  WMA,  and  other  nongov- 
ernmental organizations  concerned  with  weather  modification  are  dis- 
cussed under  the  section  on  private  organizations  in  chapter  8  of  this 

Weather Modification  Ad visory  Board 

The  National  Weather  Modification  Policy  Act  of  1976,  Public  Law 
91-490  of  October  13,  1976,  requires  that  the  Secretary  of  Commerce 
"shall  conduct  a  comprehensive  investigation  and  study  of  the  state  of 
scientific  knowledge  concerning  weather  modification,  the  present  state 
of  development  of  weather  modification  technology,  the  problems  im- 
peding eli'ective  implementation  of  weather  modification  technology, 
and  other  related  matters" ;  and  that  "the  Secretary  shall  prepare  and 
submit  to  the  President  and  the  Congress  *  *  *  a  final  report  on  the 
findings,  conclusions,  and  recommendations  of  the  study."'  14 

The  Secretary  of  Commerce  responded  to  these  requirements  by 
appointing  an  18-member  non-Federal  Weather  Modification  Advisory 
Board  to  conduct  the  study  and  prepare  a  report  recommending  a  na- 
tional weather  modification  policy  and  a  national  program  of  research 
and  action  to  carry  out  the  policy.  Members  of  the  Advisory  Board, 
with  their  affiliations,  and  the  charter  to  the  Board  from  the  Secretary 
are  included  in  appendix  K.  The  Board's  final  draft  report  is  to  be 
submitted  to  the  Secretary  for  her  approval  and  any  necessary  modifi- 
cations, after  which  it  will  be  transmitted  to  the  President  and  the 

Owing  to  the  1976  Presidential  election  and  change  of  administra- 
tion in  January  1977.  and  because  of  procedures  required  by  the  Fed- 
eral Advisory  Committee  Act.  the  Advisory  Board  was  not  officially 
appointed  until  April  1977.  Consequently,  much  of  the  1-year  allotted 
time  for  the  study  had  been  lost  and  it  was  apparent  that  the  report 
could  not  be  completed  by  October  13,  1977,  as  required  by  Public  Law 
94-490.  An  extension  of  time,  requested  by  the  Secretary,  was  trans- 
mitted to  both  houses  of  the  Congress,  and  a  bill  providing  for  such  an 
extension  was  introduced  in  the  Senate,15  but  no  action  has  been  taken 
to  date,  and  formal  action  by  the  Congress  to  extend  the  time  for  com- 
pletion of  the  study  seems  unlikely.  Meanwhile,  the  Advisory  Board 
continued  its  study  and  report  development,  planning  to  deliver  its 
report  to  the  Secretary  of  Commerce  by  June  30,  1978.  Following 
public  hearings  and  receipt  of  comments  from  other  executive  branch 
agencies,  it  is  anticipated  that  the  Secretary  will  transmit  the  docu- 
ment to  the  Congress  in  the  late  summer  or  fall  of  1978. 16 

u  SpP  d.  389. 

14  Public  Law  94-490.  Sees.  4  and  5.  (The  complete  text  of  the  law  is  included  in  app.  I.) 
»S.  1938,  introduced  Jnly  27.  1077.  by  Sen.  Warren  G.  Masrnuson. 

18  This  tentative  schedule  for  completion  and  transmittal  of  the  report  is  based  on  dis- 
cussions by  the  Weather  Modification  Advisory  Board  at  its  ninth  meeting.  Apr.  4,  197S,  in 
Washington.  D.C. 


The  Advisory  Board  has  met  formally  four  times  in  Washington, 
D.C.,  and  one  time  each  in  North  Forks,  N.  Dak.;  Boulder,  Colo.; 
Champaign,  111.;  San  Francisco,  Calif.;  Chicago,  111.;  Tulsa,  Okla. ; 
Atlanta,  Ga. ;  and  Aspen,  Colo. — combining  public  hearings  with 
working  sessions.  Subpanels  and  other  ad  hoc  groups  of  Board 
members  have  also  met  numerous  times  to  work  on  specific  aspects  of 
the  study  and  to  prepare  draft  sections  of  the  report.  At  a  hearing  on 
October  26,  1977,  the  Chairman  of  the  Advisory  Board,  Harlan 
Cleveland,  briefed  the  Subcommittee  on  the  Environment  and  the 
Atmosphere  of  the  House  Committee  on  Science  and  Technology,  re- 
lating activities  to  date  of  the  Board  and  submitting  for  the  record  a 
discussion  paper  which  summarized  the  Board's  thinking  at  the  time.17 


Background  and  regulations 

Public  Law  92-205  of  December  18,  1971,18  requires  reporting 
of  basic  information  on  all  nonfederally  sponsored  weather  modifica- 
tion activities  in  the  United  States  and  its  territories  to  the  Secretary 
of  Commerce.  The  Secretary  is  further  directed  to  maintain  a  record 
of  weather  modification  activities  taking  place  in  the  United  States 
and  to  publish  summaries  of  such  information  "from  time  to  time." 

Within  the  Commerce  Department  the  National  Oceanic  and 
Atmospheric  Administration  (NOAA)  has  administered  this  pro- 
gram on  behalf  of  the  Secretary.  Rules  for  carrying  out  the  provisions 
of  this  legislation,  published  in  the  Federal  Register,19  went  into  effect 
on  November  1,  1972.  The  rules  have  since  been  revised  and  amended 
twice — on  February  15,  1974,20  to  cover  safety  and  environmental 
aspects  of  field  activities  and  to  consider  possible  interference  with 
Federal  research  projects,  and  again  on  July  4,  1976,21  to  modify  cer- 
tain reporting  procedures.  A  copy  of  the  rules  and  regulations  cur- 
rently in  effect  appears  in  appendix  L.  In  the  same  appendix  are 
copies  of  the  forms  and  specific  reporting  instructions  to  be  used  for 
submission  of  required  information  to  NOAA  by  weather  modifica- 
tion operators. 

Reporting  requirements  include  initial,  interim,  and  final  reports. 
It  is  required  that  NOAA  receive  the  initial  report  at  least  10  days 
prior  to  the  commencement  of  weather  modification  activities.  The 
rules  provide  for  exceptions  whereby  this  10-day  rule  may  be  waived 
under  certain  emergencies  and  also  require  filing  a  supplemental  report 
if  the  initial  report  is  subsequently  found  to  contain  inaccuracies,  mis- 
statements, or  omissions  or  if  project  plans  are  changed.  The  interim 
report  is  required  January  1  of  each  year  (October  1  prior  to  the  1976 
revision  of  the  rules)  unless  the  project  has  been  terminated  prior  to 
that  date.  Upon  completion  of  the  project,  a  final  report  is  due,  and, 

17  Weather  Modification  Advisory  P,oard.  "A  U.S.  Policy  To  Enhance  the  Atmospheric 
Environment,"  a  discussion  paper.  Oct.  21.  1977,  29  pp.  (Also  appeared  In  record  of 
hearing:  TVS.  Congress.  House  of  Representatives.  Committee  on  Science  and  Technology, 
Subcommittee  on  the  Environment  and  the  Atmosphere.  Weather  Modification.  95th 
Cong.,  1st  sess.  Oct.  21,  1977,  pp.  20-49. 

18  See  appendix  I  for  a  reproduction  of  Public  Law  92-205  and  see  earlier  section  of  this 
chapter  under  congressional  activities  for  discussion  of  enactment  of  this  law  and  those 
enacted  since  which  have  extended  appropriations  authorization  through  fiscal  year  1980. 

19  Federal  Register,  vol.  37.  No.  208.  Friday,  Oct.  27.  1972. 
^Federal  Register,  vol.  39,  No.  10,  Tuesday.  Jan.  15,  1974. 
21  Federal  Register,  vol.  41.  No.  113.  June  10,  1976. 


until  such  final  report  is  received  by  XOAA,  the  project  is  considered 

Reporting  of  Federal  activities 

Although  not  required  to  do  so  by  Public  Law  92-205,  as  of  Novem- 
ber 1,  1973,  Federal  agencies  also  began  reporting  to  NOAA  their 
experimental  activities  in  weather  modification.  This  procedure  re- 
sulted from  an  agreement  obtained  by  the  Secretary  of  Commerce 
from  the  responsible  agencies  at  the  request  of  the  Interdepartmental 
Committee  for  Atmospheric  Sciences  (ICAS)  and  the  Office  of  Man- 
agement and  Budget.  Reporting  guidelines  adopted  for  Federal 
agencies  are  similar  to  those  for  non-Federal  projects,  using  the  same 
data  forms;  however,  Federal  entities  and  employees  thereof  are  ex- 
cepted from  criminal  penalty  to  which  other  operators  are  subject  for 
noncompliance,  and  no  Federal  agency  is  required  to  furnish  infor- 
mation or  material  whose  protection  is  in  the  interest  of  national 
security.  With  similar  reporting  of  federally  and  nonfederally  spon- 
sored activities,  there  now  exists  a  central  source  of  information  on  all 
weather  modification  projects  in  the  United  States.23 

Summary  reports  on  U.S.  weather  modification  activities 

Since  the  Secretary  of  Commerce  was  given  responsibility  for  col- 
lecting information  on  weather  modification  activities  and  for  pub- 
lishing "from  time  to  time"  summaries  of  this  information,  four  such 
summary  reports  have  been  prepared  by  the  Environmental  Modifica- 
tion Office  of  NOAA's  Office  of  Environmental  Monitoring  and  Pre- 
diction. The  first  summary  covered  reported  projects  which  were  active 
some  time  between  November  1, 1972,  and  March  22, 1973.24  The  second 
report  incorporated  information  published  in  the  first  summary  and 
extended  the  period  of  coverage  to  include  activities  reported  through 
December  1973. 25  Subsequent  reports  summarized  information  on 
ongoing  weather  modification  projects  underway  during  calendar  years 
1974 26  and  1975,27  respectively.  The  latter  two  summaries  include 
information  on  Federal  as  well  as  non-Federal  projects  for  the  com- 
plete calendar  years. 

An  analysis  of  the  weather  modification  activities  conducted  in  the 
United  States  during  calendar  year  1975  and  a  preliminary  analysis 
of  activities  during  calendar  years  1976  and  1977  are  found  in  chap- 
ter 7  of  this  report.  These  discussions  are  based  upon  the  latest  weather 
modification  summary  report  published  by  NOAA  28  and  a  prelimi- 
nary report  on  the  latter  2  years  prepared  by  Charak.29 

-  Charak,  Mason  T..  "Weather  Modification  Activity  Reports  :  Calendar  Year  1975."  Na- 
tional Oceanic  and  Atmospheric  Administration,  Office  of  Environmental  Monitoring  and 
Prediction,  Rockville.  Md.,  June  1976,  pp.  3  and  60. 

23  Charak,  Mason  T.  and  Mary  T.  DiGiulian,  "Weather  Modification  Activity  Reports  ; 
Nov.  1,  1972,  to  Dec.  31,  1973."  National  Oceanic  and  Atmospheric  Administration, 
Office  of  Environmental  Monitoring  and  Prediction,  Rockville,  Md..  March  1974,  pp. 
1  and  D-l. 

24  Charak,  Mason  T.  and  Mary  T.  DiGiulian,  "Weather  Modification  Activity  Reports  ; 
November  1.  1972.  to  March  22.  1973.''  National  Oceanic  and  Atmospheric  Administration, 
Office  of  Environmental  Monitoring  and  Prediction.  Rockville,  Md..  March  1973.  23  pp. 

25  Charak  and  DiGiulian.  "Weather  Modification  Activity  Reports ;  Nov.  1,  1972  to 
Dec.  31,  1973,"  1974.  40  pp. 

26  Charak.  Mason  T.,  "Weather  Modification  Activity  Reports  ;  Calendar  Tear  1974."  Na- 
tional Oceanic  and  Atmospheric  Administration,  Office  of  Environmental  Monitoring  and 
Production,  Rockville,  Md.  March  1975,  37  pp. 

^Charak,  "Weather  Modification  Activity  Reports;  Calendar  Year  1975."  June  1976, 
64  pp. 

25  Ibid. 

29  Charak.  Mason  T..  "Preliminary  Analvsis  of  Reported  Weather  Modification  Activities 
In  the  U.S.  for  CY  1976  and  1977."  (Submitted  for  publication  in  the  Journal  of  Weather 
Modification,  1978.) 


It  should  also  be  noted  that,  as  part  of  its  responsibilities  as  lead 
agency-  for  weather  modification  under  Public  Law  85-510,  the  Na- 
tional Science  Foundation  (NSF)  began  collecting  reports  on  weather 
modification  activities  on  a  regular  basis  in  1966.  Two  years  later,  how- 
ever, Public  Law  90-407  repealed  the  powers  of  the  NSF  to  require 
such  reporting.  During  those  2  years,  the  Foundation  published  sum- 
maries of  reported  activities  for  fiscal  years  1967  and  1968,  which  were 
included  in  the  9th  and  10th  annual  NSF  weather  modification  re- 
ports that  were  submitted  to  the  President  and  the  Congress.30  From 
September  1,  196S,  until  December  18,  1971,  when  Public  Law  92-205 
was  enacted,  no  Federal  department  or  agency  was  authorized  to  col- 
lect reports  on  weather  modification  activities.  During  this  interim, 
pertinent  information  on  weather  modification  activities  of  the  Fed- 
eral Government  and  on  the  status  of  Aveather  modification  research 
and  technology  was  published  in  three  weather  modification  summary 
reports,  published  at  the  request  of  the  ICAS  by  NOAA.31  This  brief 
series  ended  with  the  report  which  covered  fiscal  year  1973 ;  however, 
some  of  the  kinds  of  information  contained  in  these  reports  will  be 
included  in  the  NOAA  summary  reports  on  weather  modification 
activities ;  such  material  was  first  so  included  in  the  summary  for  cal- 
endar year  1975.32 



In  accordance  with  the  mandates  of  several  public  laws,  or  self- 
initiated  by  the  agencies  or  interagency  committees,  the  executive 
branch  of  the  Federal  Government  lias  undertaken  a  number  of  major 
studies  over  the  past  25  years  on  weather  modification  policy  and/or 
recommended  programs  for  research  and  development.  Some  of  these 
studies  have  been  performed  under  contract,  others  have  been  con- 
ducted by  committees  of  Federal  employees,  while  a  third  group  were 
carried  out  by  Federal  committees  or  panels  composed  of  non-Govern- 
ment experts.  Each  of  the  completed  major  studies  was  followed  by  a 
report  which  included  findings  and  recommendations. 

The  earliest  studies  were  conducted  in  the  early  1950's,  largely  at  the 
instigation  of  the  Department  of  Defense,  at  that  time  the  agency  with 
the  major  Federal  role  in  weather  modification.  The  most  significant 
study  and  report  of  the  1950's  was  that  of  the  Advisory  Committee  on 
Weather  Control,  directed  by  Public  Law  83-256.  There  was  an  un- 
usually large  number  of  major  studies  conducted  and  reports  issued 
during  the  period  from  1965  through  1976.  The  reports  included  two 
from  the  National  Academy  of  Sciences,  two  from  the  Interdepart- 

80  National  Science  Foundation.  "Weather  Modification  :  Ninth  Annual  Report  for  Fiscal 
Fear  Ended  June  HO,  1967."  NSF  68-21.  Aug  28.  1968.  Washington.  D.C..  U.S.  Govt.  Print. 

Off.,  Aug.  28,  1968,  pp.  75-77  :  and   .  "Weather  Modification  ;  Tenth  Annual  Report 

for  Fiscal  Year  Ended  June  30,  196S,"  NSF  69-18,  Washington.  D.C.,  U.S.  Govt.  Print. 
Off..  Aug.  1969,  pp.  111-115. 

31  U.S.  Department  of  Commerce.  National  Oceanic  and  Atmospheric  Administration. 
"Summary  Report:  Weather  Modification  ;  Fiscal  Years  1969.  1970.  1971."  Office  of  the 
Assistant  Administrator  for  Environmental  Modification.  Rockville,  Md..  May  1973.  163  pp.  : 
 .  "Summary  Report :  Weather  Modification  ;  Fiscal  Year  1972."  Office  of  Environmen- 
tal Monitoring  and  Prediction,  Rockville.  Md.,  November  1973.  226  pp.  :  and   .  "Sum- 
mary Report  :  Weather  Modification  ;  Fiscal  Year  1973."  Office  of  Environmental  Monitor- 
ing and  Prediction.  Rockville.  Md..  December  1974.  155  pp. 

32Cbarak,  "Weather  Modification  Activity  Reports  ;  Calendar  Year  1975,"  June  1976,  pp. 


mental  Committee  for  Atmospheric  Sciences  (ICAS),  three  from  the 
National  Science  Foundation,  and  at  least  one  each  from  the  Depart- 
ment of  Agriculture,  the  Environmental  Science  Services  Administra- 
tion (predecessor  of  XOAA),  and  the  Domestic  Council's  Subcom- 
mittee on  Climate  Change.  In  1966  alone,  at  least  five  reports  on 
federally  sponsored  weather  modification  studies  appeared.  The  Na- 
tional Advisory  Committee  on  Oceans  and  Atmosphere  (NACOA) 
has  also  issued  policy  statements  on  weather  modification  in  each  of  its 
six  annual  reports  to  date. 

The  most  recent  major  study  was  undertaken  in  1977  by  the  Weather 
Modification  Advisory  Board  under  the  auspices  of  the  Department  of 
Commerce,  which  has  been  directed  to  conduct  such  a  policy  study  and 
to  submit  a  report  to  the  Congress  in  accordance  with  the  National 
Weather  Modification  Policy  Act  of  1976  (Public  Law  94-490). 

The  principal  weather  modification  studies  and  reports,  sponsored 
by  the  executive  branch  are  discussed  very  briefly  in  the  following  sub- 
sections.33 The  conclusions  and  recommendations  of  the  major  policy 
studies  are  discussed  and  summarized  in  a  separate  chapter  of  this 

Studies  of  the  early  1950' s 

In  1950,  there  were  controversies  among  scientists  over  the  validity 
of  reported  results  from  weather  modification  experiments,  notably 
Project  Cirrus,  a  Defense  Department  project,  conducted  primarly  by 
the  General  Electric  Company  under  contract.35  It  was  agreed  by  those 
involved  that  there  should  be  an  independent  scientific  review  of  the 
work  and  the  claims  of  spectacular  results.  The  appointed  review  com- 
mittee was  organized  under  the  jurisdiction  of  the  Department  of 
Defense,  since  Project  Cirrus  was  sponsored  by  that  Department,  with 
Dr.  Bernard  Haurwitz  of  New  York  University  as  chairman.  The 
committee  was  to  investigate  results  and  report  to  the  Defense  Depart- 
ment; however,  when  the  report  was  submitted  in  the  late  spring  of 
1950,  it  was  classified  "confidential,"  to  the  dismay  of  committee  mem- 
bers, since  it  had  been  hoped  that  the  report  would  explain  the  real 
prospects  of  weather  modification  to  the  public.36  According  to  Byers, 
the  Defense  Department  finally  agreed  to  let  the  report  be  published 
by  the  American  Meteorological  Society,  and  it  appeared  "in  the  guise 
of  a  report  requested  by  the  president  of  the  Society."  37-  38  The  overall 
tenor  of  the  report  was  one  of  skepticism  toward  the  claims  of  success 
for  Project  Cirrus,  and  the  concluding  paragraph  of  the  report  stated 
that : 

It  is  the  considered  opinion  of  this  committee  that  the  possibility  of  artificially 
producing  any  useful  amounts  of  rain  has  not  been  demonstrated  so  far  if  the 
available  evidence  is  interpreted  by  any  acceptable  scientific  standards.38 

In  view  of  the  potential  value  of  weather  modification  techniques  and 
the  controversial  results  obtained  thus  far,  the  research  agencies  of  the 

33  Studies  and  reports  of  the  congressional  support  agencies  have  been  noted  earlier  in 
this  chapter  under  the  discussion  of  congressional  weather  modification  activities.  See 
p.  209. 

34  See  chap.  6,  p.  313  ff. 

85  For  a  discussion  of  Project  Cirrus,  see  p.  39,  under  the  history  of  weather  modification 
in  chapter  2. 

36  Byers,  Horace  W.,  "History  of  Weather  Modification,"  In  Wilmot  H.  Hess  (editor). 
Weather  and  Climate  Modification.  New  York,  Wiley,  1974,  pp.  33-34. 

37  Ibid.,  p.  34. 

38  The  report  appeared  under  correspondence,  signed  by  members  of  the  committee,  in  the 
Bulletin  of  the  American  Meteorological  Society,  vol.  31,  No.  9,  November  1950.  pp.  346-347 

39  Ibid  .  p.  347. 


U.S.  Army,  Navy,  and  Air  Force,  along  with  the  U.S.  Weather  Bureau, 
in  1951  appointed  an  Artificial  Cloud  Nucleation  Advisory  Group, 
chaired  by  Dr.  Sverre  Petterssen  of  the  University  of  Chicago.  The 
Advisory  Group  was  asked  to  make  a  survey  of  the  field  of  weather 
modification  and  u.  .  .  to  recommend  a  program  for  experiments  and 
tests  that  could  be  expected  to  clarify  major  uncertainties  that  existed 
at  that  time  for  the  operational  uses  of  weather  modification  tech- 
niques." The  Advisory  Group  found  some  support  for  the  claims  of 
Langmuir  that  seeding  had  affected  larger  atmospheric  systems,  but 
emphasized  the  need  for  clarification  experiments.  The  group  con- 
cluded that  there  was  good  evidence  to  indicate  that  cold  stratus  (and 
presumably  cold  fog)  could  be  dispelled  by  nucleation.  It  had  not  been 
possible  in  any  case  to  predict  what  results  would  have  occurred  if 
seeding  had  not  been  performed,  indicating  the  need  for  more  rigorous 
control  of  future  tests.  The  Advisory  Group  consulted  a  number  of 
experts  in  the  field  and  all  agreed  that  there  was  need  for  a  coordinated 
program  for  experiments  in  order  to  determine  whether  or  not  weather 
systems  can  be  modified  with  useful  results.40 

The  Advisory  Group  recommended  establishment  of  six  projects  to 
answer  these  questions  and  was  requested  to  remain  and  furnish  advice 
to  the  projects  and  their  sponsoring  agencies,  provide  for  information 
exchange,  and  review  results.  One  of  these  projects  was  sponsored  by 
the  Weather  Bureau,  and  of  the  five  sponsored  by  the  Defense  Depart- 
ment, four  were  conducted  by  contractors  and  the  fifth  by  the  Army 
Signal  Corps  in  house.  In  July  195±  the  Advisory  Group  met  with 
representatives  of  all  the  projects  and  sponsoring  agencies,  reviewed 
the  results  in  detail,  and  recommended  that  full  reports  on  each  proj- 
ect be  published.  Project  results  were  subsequently  reported  in  a  1957 
monograph  of  the  American  Meteorological  Society.41 

Advisory  Committee  on  Weather  Control 

The  first  major  comprehensive  study  of  weather  modification  and 
its  ramifications  was  undertaken  by  the  Advisory  Committee  on 
Weather  Control,  following  the  congressional  mandate  under  Public 
Law  83-256,  of  August  13, 1953,  which  established  the  Committee  and 
directed  that  the  study  and  evaluation  of  weather  modification  be  per- 
formed. The  Committee  was  comprised  of  the  Secretaries  of  five  de- 
partments and  the  Director  of  the  National  Science  Foundation,  or 
their  designees,  and  five  private  members,  including  the  Chairman, 
who  were  appointed  by  the  President.42  Chaired  by  Dr.  Howard  T. 
Orville,  the  Committee  forwarded  its  two-volume  report 43  to  Presi- 
dent Eisenhower  on  December  31,  1 0r>7,  after  the  June  30,  1956,  termi- 
nation date  for  the  act  had  been  extended  by  Public  Law  84—664  of 
July  9.  1950.  In  its  final  report  the  committee  recommended : 44 

(1)  That  encouragement  be  given  for  the  widest  possible  competent 
research  in  meteorology  and  related  fields.  Such  research  should  be 

4  Petterssen.  Sverre.  "Reports  on  Experiments  with  Artificial  Cloud  Nucleation  :  Intro- 
ductory Note."  In  Sverre  Petterssen.  Jerome  Spar.  Ferguson  Hall,  Roscoe  R.  Braham,  Jr., 
!    lis  J.  Rattan.  Horace  R.  Byers.  H.  J.  aufm  Kampe,  J.  J.  Kelly,  and  H.  K.  Weickmann. 
Cloud  and  Weather  Modification:  a  Group  of  Field  Experiments.  Meteorologieil  mono- 
hs,  vol.  2.  No.  11.  American  Meteorological  Society,  Boston,  July  1957.  pp.  2-3. 
Ibid,,  115  pp. 
43  Public  Law  83-256,  sections  4  and  5. 

Arlvisorv  Committee  on  Weather  Control,  final  report  of  thp  Advisory  Committee  on 
Wp.itbf>r  Control,  Washington,  D.C.,  U.S.  Government  Printing  Office,  1958,  in  two  volumes, 
22-422  pp. 

«  Ibid.,  vol.  I.  pp.  vll-viii. 


undertaken  by  Government  agencies,  universities,  industries,  and  other 

(2)  That  the  Government  sponsor  meteorological  research  more 
vigorously  than  at  present.  Adequate  support  is  particularly  needed  to 
maintain  continuity  and  reasonable  stability  for  long-term  projects. 

(3)  That  the  administration  of  Government-sponsored  research  pro- 
vide freedom  and  latitude  for  choosing  methods  and  goals.  Emphasis 
should  be  put  on  sponsoring  talented  men  as  well  as  their  specihc 

(4)  That  an  agency  be  designated  to  promote  and  support  research 
in  the  needed  fields,  and  to  coordinate  research  projects,  it  should  also 
constitute  a  central  point  for  the  assembly,  evaluation,  and  dissemina- 
tion of  information.  This  agency  should  be  the  National  Science 

(5)  That  whenever  a  research  project  has  the  endorsement  of  the 
National  Science  Foundation  and  requires  facilities  to  achieve  its  pur- 
pose, the  agency  having  jurisdiction  over  such  facilities  should  pro- 
vide them. 

National  Academy  of  Sciences  studies 

The  Committee  on  Atmospheric  Sciences  of  the  National  Academy 
of  Sciences  (NAS/CAS)  produced  its  report  on  the  first  of  two  major 
studies  on  weather  modification  in  1966.  The  report,  entitled  "Weather 
and  Climate  Modification :  Problems  and  Prospects,'' 45  was  prepared 
by  the  Committee's  Panel  on  Weather  and  Climate  Modification,  with 
joint  support  from  the  National  Science  Foundation  and  the  Com- 
merce Department's  Environmental  Science  Services  Administration. 
Volume  1  of  the  report  contains  a  summary  of  the  study  and  recom- 
mendations, while  the  second  volume  presents  a  general  assessment  of 
the  subject,  on  which  the  panel  based  its  conclusions  and  recommenda- 
tions. The  report  expressed  cautious  optimism  regarding  the  future  of 
weather  modification.  Among  its  recommendations  were  an  increase 
in  Federal  support  from  the  1965  level  of  $5  million  to  at  least  $30 
million  by  1970  and  the  early  establishment  of  several  carefully  de- 
signed, randomized  seeding  experiments,  planned  in  such  a  way  as  to 
permit  assessment  of  the  seedability  of  various  storm  types.  The  re- 
port addressed  mostly  technical  and  administrative  problems;  it  did 
not  consider  social,  legal,  and  economic  aspects  of  the  subject,  since 
these  topics  were  taken  up  in  a  concurrent  study  by  the  NSF's  Special 
Commission  on  Weather  Modification,  which  worked  closely  with  the 
NAS  panel.46 

The  second  major  study  was  completed  by  the  Panel  on  Weather 
and  Climate  Modification  of  the  NAS  Committee  on  Atmospheric 
Sciences  in  1973. 47  Sponsored  jointly  by  the  National  Science  Founda- 
tion and  the  Department  of  Commerce,  the  panel  was  given  respon- 
sibility in  the  study  "(1)  to  determine  the  scientific  and  national  prog- 
ress in  weather  modification  since  the  earlier  study  of  the  field  was 
reported  upon  in  1966,  (2)  to  consider  future  activities  that  would 

45  National  Academy  of  Sciences.  National  Research  Council,  Committee  on  Atmospheric 
Sciences.  Wenther  and  Climate  Modification  :  Problems  and  Prospects.  Publication  No.  1350, 
Washington.  D.C.,  1966.  in  2  volumes.  40+212  pp. 

46  See  discussion  be^w  on  reports  bv  the  National  Science  Foundation,  p.  239. 

47  National  Academy  of  Sciences.  National  Research  Council,  Committee  on  Atmospheric 
Sciences,  "Weather  Modification  :  Problems  and  Progress,"  ISBN  0-309-02121-9,  Washing- 
ton, D.C.,  1973.  280  pp. 


guide  and  strengthen  work  toward  further  progress,  (3)  to  examine 
and  clarify  the  statistical  design  and  evaluation  of  modification  ac- 
tivities, and  (4)  to  determine  the  current  circumstances  bearing  on  the 
increase,  decrease,  and  redistribution  of  precipitation."  48  In  its  report, 
the  panel  attempted  to  fufill  these  objectives  and  further  proposed 
the  following  three  goals  for  improving  the  science  and  technology  of 
weather  modification : 49 

1.  Completion  of  research  to  put  precipitation  modification  on  a 
sound  basis  by  1980. 

2.  Development  during  the  next  decade  of  the  technology  required 
to  move  toward  mitigation  of  severe  storms. 

3.  Establishment  of  a  program  that  will  permit  determination  by 
1980  of  the  extent  of  inadvertent  modification  of  local  weather  and 
global  climate  as  a  result  of  human  activities. 

Research  programs  required  to  achieve  these  goals  were  outlined 
along  with  basic  functions  to  be  performed  by  the  several  Federal  agen- 
cies. These  organizational  recommendations  for  the  Federal  program 
were :  "  (1)  the  identification  of  a  lead  agency,  (2)  the  establishment  of 
a  laboratory  dedicated  to  the  achievement  of  the  proposed  national 
goals,  and  (3)  assignment  to  the  recently  established  National  Advisory 
Committee  on  Oceans  and  Atmosphere  of  the  responsibility  for  examin- 
ing the  public  policy  issues  of  weather  modification,  as  well  as  the 
development  of  organization  and  legislative  proposals."' 50 

Studies  by  the  Interdepartmental  Committee  for  Atmospheric  Sciences 

Another  report  to  appear  in  1966  was  the  first  of  two  by  the  ICAS 
on  weather  modification,  which  prescribed  a  recommended  national 
program  in  the  field.51  Compiled  by  the  chairman  of  the  ICAS  Select 
Panel  on  Weather  Modification,  Dr.  Homer  E.  Newell  of  the  National 
Aeronautics  and  Space  Administration,  the  report  laid  out  details  for 
such  a  national  program  and  contained,  as  appendices,  the  earlier 
recommended  program  of  the  ICAS  Select  Panel  itself,  as  well  as 
recommendations  from  the  concurrent  studies  by  the  NAS  and  the 
NSF  Special  Commission. 

The  ICAS  completed  another  interagency  study  in  1971,  when  it 
produced  a  report  which  outlines  a  program  for  accelerating  national 
progress  in  weather  modification.52  The  report  attempted  to  identify 
national  weather  modification  needs  and  designated  research  projects 
for  meeting  these  needs  as  national  projects,  each  with  a  responsible 
lead  agency  and  support  from  other  Federal  agencies.53  Some  of  these 
projects  were  already  underway  or  in  planning  stages  by  various 
agencies.  Few  were  ever  consummated  as  truly  interagency  national 
projects  as  envisioned,  though  there  was  some  degree  of  cooperation 
in  some,  such  as  the  National  Hail  Research  Experiment  (NHRE), 

*8  Ibid.,  p.  ill. 
*»  Ibid.,  p.  xv. 

«  Newell,  Homer  E.,  "A  Recommended  National  Program  in  Weather  Modification,"  Fed- 
eral Council  for  Science  and  Technology,  Interdepartmental  Committee  for  Atmospheric 
Sciences,  ICAS  Kept.  No.  10a,  November  1966,  93  pp. 

52  Federal  Council  for  Science  and  Technology,  Interagency  Committee  for  Atmospheric 
Sciences,  "A  National  Program  for  Accelerating  Progress  in  Weather  Modification,  ICAS 
Kept.  No.  15a.  June  1971,  50  pp.  „  .    21..Aa  00.  . 

M  For  a  list  of  the  seven  national  projects  identified  by  the  ICAS,  see  p.  224.  under  the 
discussion  of  the  activities  of  the  ICAS. 


and  others,  such  as  Interior's  Colorado  River  Basin  pilot  project 
(CKBPP),  continued  essentially  as  large  single-agency  projects. 

Domestic  Council  study 

A  weather  modification  study  was  undertaken  in  1974,  following 
establishment  of  a  Subcommittee  on  Climate  Change  by  the  Environ- 
mental Eesources  Committee  of  the  Domestic  Council.  Comprised  of 
representatives  from  the  Office  of  Management  and  Budget  (OMB) 
and  most  Federal  agencies  with  atmospheric  sciences  programs,  except- 
ing the  Defense  Department,  the  subcommittee  attempted  to  assess  the 
Federal  role  in  weather  modification.  Drawing  upon  recent  documenta- 
tion on  the  progress,  status,  and  problems  in  the  field,  and  through  a  2- 
day  hearing  of  representatives  from  various  parts  of  the  weather  modi- 
fication community  and  other  interested  groups,  the  subcommittee 
prepared  its  report  in  1975.54  In  its  executive  summary,  the  Domestic 
Council  report  found  that : 

Weather  modification  represents  a  potential  tool  for  exerting  a  favorable  influ- 
ence over  destructive  weather  events  and  for  augmenting  water  supplies  in  some 
areas  where  additional  water  is  needed  for  energy,  food,  and  fiber  production ; 55 

and  the  following  general  recommendation  was  formulated : 

A  policy  should  be  adopted  to  develop,  encourage,  and  maintain  a  comprehen- 
sive and  coordinated  national  program  in  weather  modification  research  and  in 
the  beneficial  application  of  the  technology  along  the  lines  of  the  recommenda- 
tions embodied  in  this  report.56 

Specific  findings  and  recommendations  were  also  given  for  each  of 
the  three  areas  of  research,  operations,  and  regulation,  which  the  sub- 
committee examined.57 

Policy  and  planning  reports  produced  by  Federal  agencies 

Since  the  very  early  studies  of  the  1950-51  era,  instigated  primarily 
by  the  Department  of  Defense,  other  Federal  agencies  have  undertaken 
major  policy  and  planning  studies,  either  as  "in-house"  efforts  or 
through  contractors  or  committees  established  by  the  agency. 

The  National  Science  Foundation  has  produced  the  greatest  num- 
ber of  agency  policy  reports,  based  on  studies  conducted  by  its  Special 
Commission  on  Weather  Modification  and  by  contractors.  Two  reports 
appearing  in  1966  were  prepared  by  or  under  auspices  of  the  Special 
Commission,  culminating  a  study  authorized  in  October  1963  by  the 
National  Science  Board.58, 59  The  Special  Commission,  established  in 
June  1964  and  chaired  by  Dr.  A.  R.  Chamberlain  of  Colorado  State 
University,  had  been  "*  *  *  requested  to  examine  the  physical, 
bilogical,  legal,  social,  and  political  aspects  of  the  field  and  make  rec- 
ommendations concerning  future  policies  and  programs."  60  Phvsical 
aspects  were  studied  in  cooperative  liaison  with  the  NAS  panel  in  its 
concurrent  study ; 61  however,  the  membership  of  the  Special  Commis- 
sion reflected  expertise  in  the  other  aspects  of  weather  modification  not 

64  Domestic  Council.  Environmental  Resources  Committee.  Subcommittee  on  Climate 
Change,  "The  Federal  Role  in  Weather  Modification,"  Washington,  D.C.,  December  1975, 
39  pp. 

55  Ibid.,  p.  i. 

»  Ibid. 

wIbid..  pp.  i-iii. 

68  Special  Commission  on  Weather  Modification.  NSF  66-3.  1966.  155  pp. 

59  Taubenfeld.  Howard  J.  "Weather  Modification:  Law.  Controls.  Operations."  report  to 
the  Special  Commission  on  Weather  Modification.  National  Science  Foundation,  NSF  66-7, 
Washington.  D.C..  1966.  79  pp. 

*>  Special  Commission  on  Weather  Modification.  NSF  66-3,  1966,  p.  iii. 

61  See  p.  237  above. 


previously  addressed  by  the  other  studies.  Much  of  the  background 
work  for  the  treatment  of  these  other  aspects  of  the  problem  was  sup- 
ported by  NSF  grants  and  subsequently  published  as  separate  reports. 
These  included  the  biological  aspects,  human  dimensions,  international 
relations,  and  legal  aspects.  Of  these  separate  studies  all  were  published 
in  various  nongovernmental  media,  except  the  last  one,  which  appeared 
in  the  format  of  the  XSF  Special  Commission  report.62  All  of  these 
aspects  were  reviewed  and  summarized,  and  recommendations  were 
presented,  in  the  principal  Commission  report,  which  sought  to  answer 
the  following  question :  "With  the  physical  possibility  of  modifying 
the  weather  and  climate  already  partly  demonstrated,  how  by  artifi- 
cially inducing  deliberate  changes  in  the  environment  may  man  act  to 
control  or  develop  changes  in  the  atmosphere  considered  to  be  desirable 
by  society  ?" 63 

A  contracted  study  was  undertaken  for  the  NSF  by  the  Rand  Corp. 
in  1962  to  establish  the  framework  of  a  cohesive  approach  to  research 
on  weather  modification.  Part  of  the  program  was  to  conduct  a  com- 
prehensive state-o